When someone is going to do something really stupid,
useless, or annoying, or if you are
jealous that someone is getting to do something you're not, it is a put-down. See
whatever.
geek: Well, I'M going to get my hair follicle tested for carbon today!
normal kid: Psh, have fun.
Annie: guess what, i get a free
shopping spree at
neiman marcus today!!
Jenna: psh, have fun.