I've done the opening the tank thing, flashed my paper with an iPod screen (yep, they're really bright) checked my focus without a safelight, mixed up my bath trays... The ironic thing is that these things happen despite what I would consider a fairly disciplined set of darkroom routines. What really bites is when I spend the whole evening "perfecting" a print only to have the final print stain overnight because I've exhausted the fixer.