is it weird for men to wear speedos? ?

Usually either "Gay" or not confident about their "manhood" and feel a need to "Show off"

same reason why go without any at all// just wear women's tights

It is the the U.S.  In Europe many men wear them. For whatever reason they never caught on over here.

No its sexy ............

No it is not inappropriate for men to wear speedos. Swim briefs are the best sort of swimwear for men as they do not drag in the water, they dry quickly out of the water, and they give support where it is needed. Additionally if you wish to soak up the rays of the sun to develop your suntan then speedos allow this.

It IS weird if they think they're impressing women wearing a speedo.  I've never know anyone who liked seeing that - sadly, for them, we mostly laughed amongst ourselves, shaking our heads like "Ew...what was he thinking" whenever we saw someone wearing one at the pool or beach.

If the man is muscular, ripping with muscles, then it's just okay.

Not weird, but unusual. In athletic competition speedoes are white common. At the local swimming pool you see them in the lap, exercise, and diving pools and not so much in the recreational pools where swim shorts and surfer shorts are far more common. Many guys aren't completely comfortable with the high level of exposure in a a speedo so swim shorts give them the coverage they want. 

Not if your girl likes them on you.   I don't like them much but she did so giddyup

Depends on their builds.