Passing the guard without a gi? Hell, that's easy. Just bait 'em with one of your arms across his chest (keep your other hand on the inside of your elbow, ready to strip his fingers off your forearm). When he opens his guard to go for an armbar or triangle, rip your arm out while stripping his grip off your 'bait' arm with your other hand, while at the same time popping one of your knees up to split his guard. It's actually funny to watch, even guys who know it's a trap can't resist that arm just sitting there, begging to be hyper-extended. It's almost like they can't fight the urge to just go for it and hope that they're faster on the draw. Granted, this is pretty much a no-gi only move. Trying this on a guy that has a grip on your gi sleeve is probably not a good idea. . .