A rat
A phrase that is also use as a snitch, such as also the rapper 6ix9ine, people often calling him rat because he snitched on other rappers or even gang members so that he doesn't get arrested, but now he's out of jail.

But today many people use the word rat to call out any nerds who snitched on them and then later smoked them like a chimney.

Nerd: did you just insulted my gender and insulted my fictional character!? I'm gonna tell Ms. Kimmy Hed
Cool dude: Ok what ever you say pal, you's a rat anyway. hope you have  trials and tribulations.
Fucking prick! You's a rat you tryna snitch on me??? I'll smoke you!