I'm 4.5 months post-op and just started swimming shirtless this week... I told myself I was gonna watch it, keep my scars out of the sun for a year... but dang, it's hot, my new apartment has a pool, and swimming with the Under Armor shirt was getting old. I slather on the SPF 50 over my scars and reapply if I'm in the pool for more than an hour.
I had a peri, so my scars aren't prominent. There's a thin white line in one spot, but that's about it. I still do have white stretch mark scars (remnants of puberty v1.0) that I'm kind of paranoid about. They're visible upon close inspection and I think they look kinda odd, like a starburst around my nipples. But nobody's given me any odd looks so far, and I figure nobody is gonna be scrutinizing some random guy's nipples.
Oh yeah... and swimming shirtless is just as awesome as you'd imagine it to be

Swimming is easier when you don't have to wear a shirt.