The worst I've personally experienced was close to two hours at the old DTW terminal on a day with very bad thunderstorms. Part of the delay was waiting for staff to guide the aircraft it once an open gate was found after our first gate being unexpectedly occupied.

The worst I've heard of was five or ten years ago at ATL during an early January ice and snow event with insufficient deicing equipment and trained staff. My NW flight from MSP arrived early, gate was ready, and I had my luggage before our scheduled arrival time. However, DL flights were backed up badly. Some at my meeting reported sitting on the ground up to thirteen hours before being permitted to deplane using the stairs. It was a big mess.