In the past, I've actually done a lot of what the OP shared about "pretending to be one of the guys," though I've never been a natural chameleon. I tried to adjust my behavior so much to fit a hyper-masculine persona. I didn't do it so much in person (although I'd make a point about not being feminine), but I did it in every single online community I frequented. I'd change my typing to match theirs, use similar words to them, and worst of all, partake in a lot of talk about banging and rating women even though I wasn't that interested in it. I never actually pretended to like sports, but I'd specifically talk about the masculine interests I had and sports I liked (i.e. professional wrestling, metal music, etc.) and avoid talking about anything considered feminine by society.
On the other hand, I've never felt the need to pretend to be "one of the girls." It's always seemed appalling and demeaning to seem interested in stereotypical feminine interests like fashion/makeup, "boy talk," and such. I'd leave rooms whenever women talk about things like giving birth or periods because I did not want to be associated with any of it, even if I'm not even part of the conversation. In the past, I've cared too much about not wanting to be seen as vulnerable or sensitive, so I wouldn't have wanted to talk about my emotions or feelings.
At this point in my life, I've learned that I shouldn't try so hard to be seen as a male, and that I shouldn't try so hard to reject anything feminine. I allow myself to naturally enjoy things that are considered either feminine or masculine, regardless of what any group thinks. While I do still care about what people perceive me to be, I no longer want to waste my energy pretending.