Halloween

I got my start dressing at Halloween with an old girlfriend (that will have to be another post). Now that I dress on a regular basis and think I do I better good job off it what do I do? I have been invited to attend a work friends Halloween party where everybody dresses up and my old girlfriend (whom I'm still friends with and knows all about my dressing) has invited me to her party. So what do I do? Going to the work party would be good for work but wouldn't feel comfortable dressing as a girl so what would I go as. If I go to the old girlfriends party I could dress as a girl in some way. What to do? Any thoughts?