A dillo is a bottle of beer with about an ounce or warm flat beer left in the bottom of it. There are usually a herd of dillos left on the coffee tables, speakers, around the couch and on the TV after a house party. The percieved social value of a dillo and its consumption all depends on when it is consumed.
Anyone who wanders around a party dillo hunting is obviously a born loser, not worth the spit you and your drunken cadre of thug friends cover him with after he passes out and has already had his hand dipped in warm water.
You can have nothing but admiration for the guy who wakes up on the floor in the morning rolls over, lights a cig, grabs a dillo off the coffee table and sucks it down to cure his leathermouth and soften his hangover.