When you or someone are bumming are bumming so bad (for drugs, money, pussy, etc.), that you begin to act completely inappropriate, making horrendousdecisions, and likely saying some of the dumbest shit humanely possible.
Keaton: "Why won't any of these girls fuck me?"
Collin: "I'm down bad"
Keaton: "I'm so down bad right now"
Damien: " I'm mechanically down bad"
Mathew: "I'm so gay right now"