Guys... do you wear a tri-top while swimming?

I wear my Tri Top in every swim, not all guys do.

I think some go shirtless for the whole race, though that isn't always legal.

There maybe some drag from the pockets, but the tri top is designed to be slick (not as slick as a swim skin) and the compression can help reduce overall drag.

I'd wear it for the swim, or not at all.

Oh, I have no issue with being topless.  I'd race acient greece style it was allowed.

But if I'm going to wear a top on the bike/run I'm going to wear it in the swim.

Go practice your swimming sans wetsuit and see which your most comfortable with.  That's the one you go with.  Since your top is tight fitting, there shouldn't be noticeable drag.  Whatever you're more comfortable with will be better.

I have a tri-suit, so no choice for me.  Lots of guys go with both pieces.  Lots go without the top.  Some go with a classic speedo.  

Yes for Olympic or longer and/or under wetsuit.

No for sprint without wetsuit.

I wear tri suits because I'm at the sprint level creeping into oly level, thus, no need for any split. As such, being in Florida, yes, I would consider that wearing a top. My tri suit is pretty expensive and it's made for swimming in. It's dimpled and quite fancy.

I've done a few practice sessions on my own and have just used my TYR tri shorts and not a top. For one, it's quite hot here and I don't need to be wearing a top if I'm just practicing.

Whatever the case may be, ensure you have the right size. Tops should be SKIN TIGHT to prevent any drag in the water.

I generally don't wear a top and only wear a top when I swim if I've got a wetsuit on... i.e. air temps might be cool.  Anyway I've had two tips shown to me if you want to put a top on in t1.  Roll the top up and stick your head in the top pull down over your arms and you can work it on during the bike.  Other technique was do something similar but put the top down around your waist inside your shorts and pull it up heading into t1. 

I dislike swimming in a top, even if it is tight fitting and made to swim in.