When you cum on a girl's stomach and she pushes the cum down in her vagina and uses it as lube much to your surprise, disgust, and slight sexual curiosity.
Amy is such a freak she tried to give herself a Matt Splat much to my amazement and secret arousal.
A trip to a grocery store, convenience store, or gas station for the sole purpose of buying an excessive amount of junk food and sugary drinks, usually with friends. A chud run often happens late at night and ends with everyone involved hating themselves afterwards.