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!!
Phrase used by Nano community to warn against coins with fees, a.k.a. 'shitcoins' as a poor investment. Especially those which will have $40 fees after two more reward halvings or at only 6tps usage in a world of 7.8b people.