How do u nickname someone?

i have neva given any1 a nickname in my whole life. all my new friends give out soo many nicknames to like half the kids at our skool. if someone does something funny or something, how do i bring up a nickname. (i kno ppl at my skool nicknamed pelican, farie boy, egyptian, etc) so how do i give someone a nickname of them knowing it or not, but by being cool & not nerdy?