It’s a thing in Marvel fandom, where this particular screencap of Captain America got tagged with how his shoulder-to-waist ratio is exactly like a Dorito chip.
It got incredibly popular and spouted a bunch of artists to do fun pieces like “How to Draw Captain America. 1. Draw Dorito —>” and then the artist would have a Cap appear out of nowhere.
So the fact that RDJ called Chris Evans a Dorito now is just super funny, like they know all our silly nicknames.