Thanks for your answers, everyone. I've concluded that crop tops only look feminine if the chest is the main part being covered. And long-sleeved crop tops look feminine because they don't look functional. Functional dress = masculine. When showing skin in warm weather, a man would normally want the convenience of short sleeves before anything else.
@MartinTheFirst I want to buy a crop top now. Something that shows just a little bit of tummy and has short sleeves. Would look nice with shorts. I'm not sure where to order from though. Lol. The shops here don't sell them.
@VeganYogi I think you want to be relatively skinny and probably muscular for it to look good as a male though, otherwise it might end up looking weird again. However, you could make one yourself, just take a short sleeved one you like, cut it where you want to, fold it up, and sew a bit, or take it to your local seamstress
@MartinTheFirst Good idea. Yes. I got a slight tummy recently due to the stress of working and studying. I'll wear a crop once I get back down to a flat tummy. It's autumn now so I have many months before crop top season.
Times change. I have seen a picture of people swimming 130 years ago. The men and boys all wore the same heavy two piece swimming costumes as the ladies.
They look feminine because it is a piece of clothing similar to a bra. also don't think it's very masculine for a man to walk around showing his belly button with his clothes hanging halfway down his belly.
@uikakarotuevegeta You could be right! Although, their bellies usually stick out because the wifebeaters are too small for their large bellies rather than them wanting to show their bellies. Lol.