Mike: Dude, after my shower I was bending over to grab my boxers and my butt hit some other dude who just got out of the shower Phil: Oh, so you had a Splash Down
(1)when you have the shits so bad that the turd-el-wave splash the water out of the t-bowl
(2)The jet of water that shoots up your ass when you launch a rocket off in an airport bathroom.
To unintentionally urinate whilst sleeping, commonly caused by excess consummation of alcohol. Believed to originate from military slang and often associated with Scottish people.