PD16. Thematically challenged

For The Limericist, finding new dirty subject matter is becoming difficult.  I've covered a lot of territory in the last 3½ months so don't be surprised if a sense of deja vu occasionally hits you.  Here's one I found that sums up the problem rather well.  (I trust that line 4 isn't true...)

Beware of the limerick bore.
From a seemingly infinite store,
He trots out more verse
Where the scansion gets worse,
But the subject's the same as before.