I understand the potential for self consciousness, but you concerns likely have more to do with the SpotLight/Transparency Effect than being any sort of giveaway if the rest of your presentation is solidly masculine. I have been on a typical transition level HRT regimen for 9 years. The only comment I get from anyone about my 34B breasts when I go without a shirt is that I have "great pecs." That said, my female alter turns alot of heads when she wears a bikini at the beach. With as common an additive as estrogen has become, and the general tendency of people to be overweight, more and more guys have Gynecomastia and manboobs. The only person who would likely notice, or for that matter care about, your nipples is you.