Frogs are benign, considered ugly and slimy, undesirable. In several mythos, though, they are said to have hidden talents or wisdom and end up teaching lessons; they're something dismissed as unimportant until you least expect it.
He'd found the accurate comparison between him and the amphibian eerie as a teen and accepting and proud of it as he got older.
Even as a soldier, an Army Ranger before he was an agent with SHEILD, he was always overlooked and seen as nothing special. He found a rather vicious joy in proving all of the presumptuous dicks wrong when it hurt them most, even if his face didn't show it.
He'd always been rather solitary, a background character, but for a long time he did it out of necessity more than the desire; he understood and sympathized with Rogue of the X-Men and they talked quite a bit through e-mail despite the rivalry and grudging cooperation between their two groups.
At twelve he'd gone swimming with some neighbor kids and one of the older boys had held on to him at one point, wrapped his arms around him and pulled him to his chest as the others had stolen his shorts. He didn't know what was happening as the boy dropped minutes later, his body twitching as it tried to get paralyzed muscles to work, and died in front of them before anyone could get help.
At fourteen a girl he'd liked had kissed him and he'd kissed her back but shortly after she began having trouble breathing-she died at the hospital thirty minutes later.
After those two incidents and a couple others he stopped letting people touch any parts of him that weren't clothed.
At sixteen he met a girl with copper-black eyes and rough grey and red scales shifting over her skin and sharp points poking through her hair at the back of her head as she broke into the neighboring house and came out with a knapsack full of stolen food. Running into someone with the same abilities as him was different but it allowed them both to learn more about themselves. He was living in foster care, never knowing anything else, and her father had died when she was young, protecting her and some other souls from a rogue Shade, a Demon, leaving her on the streets. Neither of them knew much about what they could fully do except for what came naturally.
It was the first time either of them learned what species their other selves were-that was when he learned why people died if they touched him long enough.
It wasn't until he was seventeen that he learned to pull back the poison that lived in his skin, everything else he'd known to pull back, known no one else'd looked like that, could move like that, but his skin still sweated poison instead of water and salt and he'd never noticed.
Part of him felt guilty for the people dead at his hands, but another more rational part told him he was just like the mutants Xavier took in, with gifts he couldn't and didn't know how to control then.
Close to twenty years later and he could control it almost without thought.
He still didn't let anyone touch his skin without his knowledge or permission.
Meeting Clint and Natasha, being closer to them than he had anyone else besides the woman who'd become his sister at sixteen, changed that. He trusted them to read his body language and know when it was okay.
Stark didn't get close to him if he didn't have to; threat of a taser and drooling while watching supper nanny secured that.
Thor tried to crush all of their bones when he hugged them; Phil honestly didn't know if the poison that was naturally part of him would even affect the God of Thunder.
He hadn't known Captain Rogers long enough before he was stabbed to see how he'd treat him after Phil got his hero worship under control.