When you and your lady are getting ready to do the dirty, you tell her to wait for just a minute while you step out of the room. When you return, you are wearing a lobster suit. Instead of intercourse, you simply run around the room wailing, "Whalla-walla-wallah!". Your current girlfriend should be left dazed, confused, and unsatisfied. Shortly after this stunt, jump out of the window and drive away.
Warning: You will probably be seeking a new girlfriend afterwards.