Already hate Heatran because of RNG
Ok, I need to vent here a bit.
RNG is a huge piece of shit! I managed to get the chance to catch a weather boosted 100% Heatran from my raid. I had like 12 premier balls to try to catch it. I had both gold medals for its typing. HOWEVER, NIANSHIT DECIDES TO MAKE ITS HITBOX SMALL, WHICH MEANS I LEGIT FAILED TO GET A SINGLE EXCELLENT THROW ON IT!!! I LEGIT THREW MY PHONE ON THE GROUND, AND I THINK SOME PEOPLE STARED AT ME. I am 2/4 Heatran in, and that hundo Heatran that ran from me is going to haunt my dreams. Thanks, RNG, yah fucked up my day now.
Edit: I didn't actually break my phone since I was standing on grass (thankfully). Also, I actually feel upset that people say I need therapy. Not my fault I have anger issues and saying that makes you sound like an asshole.

Answers
My first shot at a perfect legendary was a boosted Latios, and I didn't get it. Do enough raids and you'll do another.
But if the game makes you so mad that you're pitching a fit and making a spectacle of yourself, perhaps you should consider backing off the game for a bit, and/or getting some therapy.
Could have worse things run on you. I lost a hundo Rayquaza on my fiancee's account due in part to only having 8 balls to catch it and not having a gold dragon medal at the time. It still hurts, but being a well adjusted adult I didn't sperg out and make a public spectacle of myself.
You'll get your chance at another perfect legendary later. On Zapdos day I made up for it by catching her a hundo weather boosted Zapdos and during the ultra unlock week I caught myself a hundo Articuno.
Having a perfect run on you sucks, but it's not the end of the world. Besides, the performance difference between the same Mon at the same level with 100% IVs vs 80ish% IVs is negligible. I've had perfects of Rayquaza, Latios, and Mewtwo (during the month of it's mass release) run on me. Each instance stung, but nothing to freak out over. Sometimes you get em, sometimes you don't. I threw 14 balls at that Rayquaza (all excellent curves with GR) and it still wouldn't stick.
I'd say the biggest takeaway from these kinds of situations is to take some deep breaths, and try to calm yourself as much as possible. Throwing at legendaries is rough if you're nervous. But even if you don't succeed, don't let any Mon give you a reason to throw and potentially damage a phone worth many hundreds of dollars.
The other takeaway, in addition to deep breaths and perspective, is to practice your throws. He doesn't have a small hitbox. He just has a standard one after the giants that were Lugia and Ho-oh.
(FWIW, the anger management is a great idea. You may have seen our resident troll and how far he's devolvee.)
I sympathize with you here. I've never had a raid 100%. I don't have any meta-relevant 100's either. I've hunted for them, I've been in discord for the community days, etc...
If I missed one when I finally get it, I'd be really frustrated. Maybe not phone-throwing, but it would sap my desire to play.
To everyone else posting - it's not about the difference between 91% and 100%. It's about having that one perfect Pokemon. Through all the raid days you hear person after person after person exclaiming that they got a 100%, and after all this time you don't even have a hundo registeel, let alone a meta-relevant one. Maybe once you have your first it's more bearable, but getting that first one to run from you would surely hurt. It's the collector that I'm sure is in all of us - almost none of us will be players with huge collections of amazing Pokemon, so having that one legendary 100% that you can max out and know that no one else has better? That's the goal. I don't need all of them, but getting one would be cool. Having one right in front of me run, that would be an awful feeling. A feeling that there's really no reason to have - shiny has a guaranteed catch at 1 in 20 some odds, why not 100% at one in 216 odds?
They do that for shinies because they know people actively hunt them - they're visibly different in most cases to where even a casual could pick one out. Imagine the asshurt that would stem from the community if it was possible to have a shiny legendary flee on you after a dozen+ excellent curve GRB'd throws. Their social media feeds would turn into dumpster fires and they were smart enough to nip that preemptively.
I don't want guaranteed catches for hundos. I say this as someone who had what would have been my crown jewel of hundos (Ray) flee on me - which again, was the first hundo legendary I ever encountered. When I caught the Zapdos I had no clue what its max CP was at regular levels, let alone boosted. Having caught it after some nail-bitingly terrible throws and checking it later to discover it was a hundo was so much more exciting than had it just been given to me. Same for the Articuno later, though I did have an inkling it was at least close to perfect before catching it.
IVs are a much smaller thing that allow hardcores to slap their dicks on a table and break out the measuring tape. Shinies can be bragged about from afar. That's why the latter is a guaranteed catch and the former isn't.
And if you caught the zapdos on the first throw, you'd have felt equally excited once you appraised it.
I think most players feel relieved when they finally catch the legendary after many failed throws - not excited. Legendaries are so common that there's no reason to get excited over any single catch - outside of a hundred or shiny.
Most players may not notice a hundred, so how does it hurt them to catch it on the first throw?
If anything, I'd argue your missing the Ray makes you biased against it though. You've missed the best, why shouldn't others?
Unlike everyone else here saying to get anger management classes and BS (which is exaggerated, not needed, and condescending), I totally feel the frustration. If I were in your shoes, I don't know how sad I'd feel, and I don't know what I'd do. Personally though I'd be too cheap to break my phone because I'm poor. If I'm rich I'd break all the phones on the ground.
poo shaped sponge-hats will manage that, even an average one.
Just in case what you said was not in sarcasm (since sarcasm doesn't really come across), you can fight me if you want, I maintain my stance, and I would advise you to take grade 12 English 30-1, and then reread my comment about breaking phones.
People here just wants to pat themselves on the back when you make a post like this. There are a couple posts thats understanding and sympathize, but most is all about:
Oh shit you messed up? well I didn't.
My (blank) is bigger and better than your (blank). Even my kids' (blank) is better.
You need halp, plz stahp, be adult cause I'm adult and you are not, so be adult, but I'm still better.
It obviously feels bad, but there's always a bright side to everything. Let's analyse the full picture here:
Heatran has just been released.
It has awful moves.
It's shiny form hasn't been released yet.
If you had caught it, you would be spending 194k dust + 220 candy only to use it in PvP, then failing to be competitive, and ultimately spending another 100k dust and 100 candy to unlock the 2nd charge move.
Only to see how Niantic, in 1 year from now, will be releasing the same Heatran, in shiny form and with a new attack which would actually won't suck, that your 100% fully maxed out and upgraded Heatran won't learn.
So basically you just dodged a bullet here.