the phenomenon wherein one seems absorb the altered states of one's companions, and begins to display the behaviours typical of the chemical in question.
"hey, you're talking at a million miles an hour and dancing to the beat of a dripping tap... but you're the only one here who hasn't taken anything!"
"hmmmm... must be chempathy. HAVE A GLOWSTICK!"
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.