Here are some possible English equivalents depending on the context:
As a term of endearment:
* Bro
* Dude
* Mate
* Buddy
* Pal
As a derogatory term:
* Bastard
* Scoundrel
* Rogue
* You rascal
It's important to note that "saaley" can be a very loaded term, and its meaning can vary greatly depending on the speaker's intention and the relationship between the speaker and the listener.
It's best to avoid using "saaley" in English unless you are very comfortable with the nuances of Hindi slang and the social context.