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OwnerOfMany Not all guys 'want something' out of the compliment, but Many do! - that's something to keep in mind.
There's nothing wrong with complimenting someone else. Are the people doing it because the other person is female/male? Are they doing it for other reasons? Might not ever really know.
I am willing to bet many guys don't take compliments too well, either.
Is it that, or something else into that?
I would probably find a question like, "Excuse me, but how can I pay you a compliment without offending you?" to be a good pick-up line.