Way back when in 2010, first time we flew into Heathrow on the A380 - the number escapes me, it was the first SQ of the day.
Anyway, upon arriving at T3 back when there were only a few A380 stands and after a bit of waiting we were told that another aircraft had got our gate and we'd have to go onto one with only a single air bridge. Sure enough the three bridge gate next to us had a SAS 737-600 plonked on it. Once the doors were opened it took an eternity to get off, first all the premium cabins then the lower deck economy cabin and then the upper deck economy cabin (where we were), someone however decided that us unwashed economy passengers weren't allowed to walk through the premium cabins to leave so we had to slowly filter down the spiral staircase at the back before walking the full length of the lower deck. All in all it took about an hour to get everyone off. Thankfully those things don't happen very often!