To be exact, Captain America is "Old Man" (who is technically 70+ years old), as well as "Capsicle" (due to his status as a Human Popsicle). Thor is "Point Break" (because of his long blond hair and beard, which look similar to Patrick Swayze in that movie). Hawkeye is "Legolas" (being an archer). Loki is "Reindeer Games" (due to the helmet) and "Rock of Ages" (due to his regalia). Loki's staff is "the Glowstick of Destiny" (which glows and mind controls people).
He keeps doing it in Iron Man 3, with names such as "Ponytail Express" and "Westworld".
and keeps going in civil war calling new kid spiderma "underoos"
•Phineas and Ferb's Dr. Doofenshmirtz mentioned he loved giving nicknames. He calls Perry "Mr. Duckbill Face", and Major Monogram "Monobrow" ("because he has...that thing where..."), and he calls Carl "Dr. Coconut."... ("Yeah. Sometimes, I wish I didn't know so much.")
Jeremy is like this with many people—except his girlfriend, Candace, who worries about the fact that he hasn't given her an Affectionate Nickname. Until he tells her that he just likes her real name.
In Teenage Mutant Ninja Turtles (2012), Michelangelo coins the name for most villains and some equipment (such as the Turtle van now being the "Shellraiser"), to the point of total annoyance. Indeed, he even gets annoyed when people decide to create their own monikers (e.g., "He calls himself the Rat King"), when or another Turtle does so.
Resident Cloud Cuckoo Lander Fred of Big Hero 6. This is the In-Universe explanation why Go Go Tomago, Wasabi, and Honey Lemon's names sound so silly. He gave them their nicknames, and the names kinda stuck.