I suffer from a mild case of gyno myself, it's not a lot but enough to get made fun of for. If you're looking to hide your gyno wear a tight undershirt, trust me it works. I'd recommend either one of those compression garments or a really tight t-shirt which is what i usually do. Another thing is to wear dark colored shirts or shirts with logos across the chest. Now I know you're worried about pushing your gyno out further but I lift weights frequently and am well built but I still have gyno, in my opinion lifting weights and making the rest of your body fit and defined helps to supercede the gyno.
And the teasing thing, trust me, you're not alone as you already know. I'm 5'7 147 lbs and I'm not fat at all but I have puffy nipples and it sucks. Man boobs, b!tch breasts, titties, cleavage, yeah i've been called it all. Another thing I would recommend is if you're looking into getting stronger without gaining too much muscle to push your gyno out is wrestling. I did wrestling earlier this year for my school and it was sweet. Not only did I get to kick the crud out of people but I gained more defintion since I burned more calories than I could count from it. Wrestling will help you get mentally and physically tougher, believe me. And on top of that you'll lose lots weight because it is an intense sport. It will also build up your confidence a lot because wrestling teaches how to fight, not that I'm condoning fighting kids who pick on you, but 90% of all fights do end up on the ground. It will teach you your own limits and help you to grow as a person.
If anyone wants to chat my AIM screename is
puddin b0y