I compliment men on their fashion sense or style. If I see a man with a very put together look, especially if it's unique and a bit out there, I will definitely compliment him. It's not "thanking the sweatshop kids in Vietnam", it's more about the thought and artistry that went into putting together a look. It has to be something unique. If he has really cool tattoos? Compliment. If he has long hair and it's a good cut? I'll compliment.

I do the same for women.

I don't think you should compliment people on their body parts if you don't know them, unless you mean to be taken as flirting.