"Nice guys finish last" is an idea that those with good morals ("nice guys") are less likely to succeed ("finish last") than those with bad morals or intentions. It often refers to dating, suggesting that people would rather date those who are mean to them than those who are nice.

In a literal sense it means "People who are unwilling to cheat/do immoral things come out behind those who do" "Cheaters win" This is used however when talking about relationships from men because they believe some women date men because they're the stereotypical 'bad boy' and the object of their affection turned them down because they didn't meet that stereotype A funny song talking about it would be this https://www.youtube.com/watch?v=2Fz3zFqLc3E

额，好像不是吧

好人优先？