When I started out, I didn't feel like I was really accepted in the music or comedy communities, and I was somewhere on the edge, but now I feel like I'm accepted in both, which is extremely gratifying.
In fact, when I come up with an idea for a parody I try to resist the urge to Google the idea to see if someone has done it already because the answer is almost always, "Yes, of course they have, they've thought of it!"
When I was a kid, I thought I was going to be an architect, because when I was 12 years old I had a guidance counselor that convinced me that that was the best career choice for me.
I start with a comprehensive list of all the recent songs that have been big hits - and then I go down that list and see if I can come up with funny ideas for them. I can always come up with ideas, but not necessarily good ones!
It's hard to really articulate what the parameters are that make one song parody-able and another song not, but if I can come up with a good enough idea for it, I go for it, and if not, then I have to move on.