For me it depends on the situation. In a school environment with my best friend I will be myself because she has known me forever and it is pointless to restrain myself. She's kind of a cynical person in the first place so I don't ever mind when she pokes fun at me, most of it having to do with my height. When I am not in her company but with my good male friends, I find that I don't restrain myself very much either. My "profession" is art so I can get away with a lot of "feminine" behavior while still having them view me as male. Occasionally we kind of "contest" each other in our masculinity, and I have taken to calling one of the guys in my group "Pretty Boy" because he is kind of fashion-conscious compared to the other guys in the group. So basically if they poke fun at me, I find room to do the same to them. The guys I hang out with are fairly masculine but they do have their "feminine" quirks which I subtly encourage in them. All in all I don't have extremely feminine mannerisms though. Like Kreuzfidel mentioned, most of the times that I've been harassed for my behavior was back in the day when I was presenting as female and people found me too "insensitive" or something of the sort.
However, in school situations where I am with people I do not know and who perceive me as male, I end up taking caution with how much of myself I express because I am afraid I might do something to make them realize something is off. Usually I tend to brush off interaction almost completely with them. This is also true of when I am just about outside of school and people perceive me as male. At this point I feel insecure about my ability to pass during any extended interaction with someone, and so I do whatever I need to in order to compensate so that I remain perceived as male. I think when I am further along in my transition and am completely comfortable with my passing ability I might be a bit more loose, but for now I don't really mind having to compensate since I am not much of a social person anyways.
As far as my style of clothing, that is what I feel I need to restrain the most. This is mostly because where I live people tend to be very traditionally dressed in stereotypically male or female clothing, and anyone who isn't really stands out. I noticed the contrast between where I live and the other day when I was at the Dali museum in St. Petersburg, FL, where there was much more variation in the ways people dressed, especially males. There was a lot less pressure to be completely masculine. If I had my way I would probably dress in a more androgynous style that still reflected a masculine personality, but where I live I find myself curbing my wardrobe, and when I am looking to buy new clothes I have to ask myself "would I get made fun of (or worse) if I wore this?". I've been called things like a ->-bleeped-<-/freak/etc. before at my school when I wear some things I own even now so the possibility of me being harassed or worse is definitely probable, and I look to avoid that. I'd rather not have to deal with hateful behavior so for the most part I dress kind of nondescriptly. However, on days when I feel up to it, I'll wear something less stereotypical and deal with any looks or confrontations by changing my behavior to something a bit more "stony" in a sense so that people can't get to me.