Yes, there are a ton of cliches out there that could never happen in real life, but the worst one, to me, is climbing through ductwork. MOST ductwork isn't big enough to hold a human body, there is so much crap (dampers, louvers, etc) inside that keeps people from climbing through uninhibited, ductwork is without exception dirty dusty and filthy, and the average piece of ductwork would hold an average weight adult man for about 2 seconds...
only in Die Hard does it not piss me off, and that's because the movie itself is awesome.