They are def. stretch marks. They are permanent because they are like a break in one of the layers of the skin, but they will get lighter. My husband has them in the same spot from lifting weights when he was younger. Now they are not pink just looks more like scars.
As far as them being off putting... If someone you are interested in can't see past the superficial, then I would say they are not worth your time and effort. Everyone has their own tastes, but I find stretch marks are excepted on guys than girls.
Those are stretch marks I got them in the same place plus my arms and legs. I got them back in my hardcore work out days, nothing to worry about. I can't imagine anyone ever having a problem with those, besides evrey time someone has made a comment about mine it has been along the lines of how big did my arms/chest used to be and my max etc. Which I like now because I have shrunk considerably since my spinal surgeries.
Stretch marks will act just like a scar does, which means it's not going away. This is not my opinion, but medical fact. Spend 10 minutes on legit medical sites researching it and you'll see. The good news is that getting stretch marks on the armpit area is very common for guys, and not necessarily caused by excessive fat. Athletes and weightlifters tend to get them a lot. In time, the color will fade, so you won't be able to see them as well. But they're not going away. All these girls with the remedies of creme and tea bags are mistaken, those will do absolutely nothing.