It's a reference to the famous red/blue pills from the matrix series, but at the same time having a simple meaning which is to chill. The phrasing is just cooler to say.
Some people can't help it; they want to fight for no reason. These people need some chillpills.
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.