When I'm in a relationship I compliment my SO very often. I tell them they're handsome and sexy, and also say more specific things such as having lovely eyes etc. I compliment their clothes as well. My last SO always made an effort with his appearance, so I made a point of noticing and appreciating it.

Apart from SOs, I compliment the men in my family fairly frequently, and almost never compliment other men in my life. I find that men have seemed to feel very uncomfortable when I've done it, so I avoid it. For example, I have a friend who I've always found attractive, but never mentioned it because men seem to interpret compliments as interest and he didn't appear to be interested in me. (Experience tells me that men get weird with unrequited feels and interpret everything as me being in love with them.) But we met up after not seeing each other for ages, and he'd clearly made a huge effort to lose weight and tone up, so I said something along the lines of "wow you look great!" And it was so awkward. He looked at me like I'd grabbed his junk.

Perhaps I just need to work on my delivery?!