If you cannot get past your self-conscious preoccupations, you have already lost a great deal of versatility as a game master. Interestingly enough, I used to play female characters with relative frequency, and as a DM I have never had problems with their portrayal. Granted, I have to accept that some aspects of the feminine mindset will always be a mystery to me, but people are people, and plenty of source material for characterization can be found all around me.
In my earlier years of gaming, crossgender play was quite common... but then, female players were few and far between and always played female characters. Then, seven or eight years ago, one of my female players decided to play a male elven character. The group was a large one, and very mixed, and her PC was never feminine... but her portrayal of an elf wasn't volubly masculine, either. In any case, it soon led to a great deal of confusion, as people tended to mix up their pronouns and miscommunicated numerous intentions and directives. After this debacle, I gently encouraged my players to retain characters of their own genders for a time... and it apparently stuck. Nowadays, my players, many of whom are roleplaying purists, simply assume that their portrayal of their character will be more accurately perceived by their peers if they avoid the crossgender complication. It is, after all, in the reception and imagination of your fellow players where your character truly comes to life....
The only awkwardness of the type described above that has ever arisen in my games had nothing to do with actual genderbending... quite the contrary. As I said, many of my players are purists, utterly devoted to the development and portrayal of their character(s). Well, I am a DM about 90% of the time, and it was an unusual occasion in which I overheard my mother, who has been one of my better players for much of my twenty-year gaming career, admit to the DM of a game in which we were both involved that her character was possibly attracted to my own... a course they mutually decided, to my amusement and relief, not to encourage. How's that for an unusual dynamic?
On a side note.... Interestingly enough, back when both of my parents played, they frequently played siblings but never lovers.... Their characters just never seemed right for each other.