There once was a [person] from [place]
Whose [body part] was [special case].
When [event] would occur,
It would cause [him or her]
To violate [law of time/space].

A friend of mine linked me to a site on the Wayback Machine that included limericks of all kinds. Here are two, but you can find more here.

There once was a buggy AI
Who decided her subject should die.
When the plot was uncovered,
The subjected discovered
That sadly the cake was a lie.