A man went into a drug store, pulled a gun, announced a robbery,
and pulled a Hefty-bag face mask over his head -- and realized
that he'd forgotten to cut eyeholes in the mask. 

I prefer to shop at a convenience store than a supermarket. The
super market is a huge commitment.  Where a convenience store
is like a one night stand.  Play it safe though, if you take
the condom wrapper off those sandwiches at the convenience
store you will pay a price.

Sent by Jeff

One student was stuck and wrote: The proof of this is
left as an exercise for the reader.
The prof wrote: Did it, fell for a non sequitur and made a 
minor calculation error. You get a B+.