1.You'd better not ask for trouble.
你最好不要自讨苦吃。

8'

ask for寻求

2.It's better not to ask him why.
最好还是别问他为什么。

25'

h的穿音

3.You don't wanna do this.
你最好别这样做。

9'

wanna=want to

4.You don't wanna mess with me, trust me.
相信我，你最好不要惹我！

19'

mess with 招惹，打扰