This occurs when friend has been drinking and randomly urinates (or urinates to put out a fire) and you accidentally briefly gander at that person genitals. The linger time between you gandering at the genital and walking away is classified as "the five second whoopsie". Any longer and you are staring.
Andrew: I have to leave, I must pee out this fire now!
Matt: Oh no! I'm getting out of here! I took a "Five Second Whoopsie" on that one.