Gag Writing Help

I've drawn a cartoon of two nerdy guys talking to each other. The caption is Nerd Yo Mama Jokes. I'm stuck and I need some help.

The first guy says, "Yo Mama is so fat, that when I ran past her I was slung 200 years into the past!"

The second guy responds, "Oh, yeah! Yo Mama is so (insert negative characteristic here) that (insert humorous metaphor here)"

In keeping with the spirit of the caption, the insulters and the first insult, the metaphor should be a bit of a sci-fi, comic or somewhat nerdy cultural or scientific reference. The first guy's insult is based on Star Trek physics (using the Earth's gravity to slingshot into the past).

The original version of the cartoon featured a fat person and someone saying that they need to go back in time so they will run by the fat person. Then it evolved into a guy saying the first insult to a second silent character but then I thought it would be funny to have the two nerdy guys trade "Yo Mama" insults.

So, I turn to you, the reader, for some help. Some of you are UUs and judging from some of the responses to Making Chutney's post http://www.makingchutney.com/2007/09/25/how-should-uus-take-names-in-vain/ a few of you have some nice comedic chops. We can make jokes about our religion and write our own material instead of letting Garrison Kiellor (not a UU) do all the work.

What's in it for you? One, the winning entry will see their wit on display in about two weeks when I actually post the cartoon. Two, the winner will receive credit on my page and in the cartoon itself. Three, the winner will have the original artwork for the cartoon sent to them. That's right, if you can finish my gag, you will receive the 8.5 x 11 inch piece of paper that I drew the cartoon on. The paper has my handwritten notes outside the border and an incomprehensible graph on the back. Everyone wins with their wit immortalized on my blog. UPDATE: Deadline - 2 weeks from the date on this blog entry. Send in the wit.

Please share your nerdy Yo Mama joke in the comments. My second person needs dialogue.

Thank you.