I don't have a favorite line, but this copypasta always comes to my mind when I think about Kif:

I used to have 50,000 posts on a fucking really weird, small, Futurama forum. There were only about 50 posters on the entire board.

For some reason I literally roleplayed as Kif (the frog who was a slave to Zapp Brannigan) in every single fucking post. I remember that the other posters would say things like ‘post your penis again for me Kif’ with a picture of Zapp and I would do it (after using photoshop to make my dick green).

I was basically a fucking sex slave for 50,000 posts. I remember on one occasion a girl came onto the board and I really liked her, but instead of talking to her like a normal human I tried to pick her up by writing an extensive, 1200 word post describing the backrub I gave to Zapp Brannigan.

I hate that part of my life almost as bad as I hate this current one.