Three women, a blonde, a brunette and a redhead get on an elevator in an office building. The doors close, and the brunette notices a suspicious-looking stain on the wall of the elevator car, about waist high. She leans down for a closer look and says, "That looks like a semen stain!"
The redhead leans down, sniffs it gingerly, and declares, "That smells like a semen stain!"
The blonde leans down, licks it, and states, "Well, it's nobody from this building."