I am thin,
I am not stout,
Because I let my gasses out.

I put this on Facebook and was honoured by a few replies:

I am stout,
I am not thin,
But I don’t keep my gasses in. (Richard Pinner)

Let them out,
Let them out,
Spread those gasses all about! (Me)

It’s too late,
It’s too late,
My methane’s making me inflate! (Roger Foyster)