I am a true introvert and nerd at heart but I fake being an extrovert really well. Fortunately I got married and had kids young, so loneliness is not even a possibility for me now. My wife is a huge extrovert and expert on human behavior so she has helped me a lot. As for what really makes me happy, learning something new (usually compsci related) always seems to excite me. Also I love cooking, writing and recording music, or calligraphy and art, stuff like that. I have no problem performing music in front of large audiences but if I had to make a speech, I'd choke.

Truth be told, I hate parties and large crowds and people in general piss me off, but I think it's bot a bad idea to fake extrovertedness. People are generally unaware they of the difference.