When you fall into the toilet because someone, usually a man leaves the seat up. Woman in particular assume the toilet seat will be down and never look before they leap into the bowl.
What the hell, I was in the bathroom and I got an assdip!
A insult describing someone who has a phobia of defacating with there butt above the water because of the possibility of water being splashed on their butt, so the person submerges their butt into the toilet water and defecates in that fashion.
"I saw Timmy pooing and I have descovered that he is a dipass, his wet boxers reveals the truth