A staple of any good mafia movie is when one of the guys rats out someone for fun and/or profit.
And guess what? Chinese has an awesome phrase for a situation like that, too!
你出賣我！（nǐ chūmài wǒ）
出賣 is actually a set phrase which, aside from meaning quite literally “to sell”, also means “to sell out/betray”.
You can also 出賣朋友, too, but that’s not really all that nice to do is it? 😦
It’s super fun and versatile to use, and I totally recommend you try using to joke around with your friends.
It’s also used in the name of a song, too!