It is a good idea, but a medium cucumber would be better. I have done that before as a joke. Rub up against girls in very crowded bar and just act like you are looking for other people or something. Girls wig out. Some are blown away by it and they like the humor. It is a great joke and conversation starter.
Another good one I do is to throw down a condom in a wrappy by my friend's feet. Do it on the side of them that has a free arm, like not holding a drink. Wait a few minutes and then point out to the girl that her romeo just dropped a raincoat from his pocket. Most girls will get all worked up. Great one!