To ejaculate in such a quiet or subtle way that your partner either barely noticed or did not notice at all.
girl: why did you stop?
guy: rolls off
girl: WTF. Did you cum?
guy: yeah
girl: I couldn't tell. That was quiet.
guy: Like a ninja. I guess i ninjaculated.
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.