Viagra for tennis strokes

I had a couple small errands to do during lunch so I found myself taking a little walk around campus. Passed by the tennis court. A couple of really old guys were playing tennis at the Stanford courts. One of them hit the ball into the net. "Where's my Viagra? I can't get it up," he said. No one else there said a thing, so I'm guessing they've all heard it before, but I found it amusing.