This one isn't me but is courtesy of a lab mate this week.
They were expressing concern of not seeing any bands in their DNA gels and in an attempt to troubleshoot asked me if I'd had any problems. Other than "shit" results and slightly faint bands (from having changed the running buffer) I couldn't really help. Labmate pointed out he couldn't see the DNA ladder either.
This happened a total of three times. I asked if they had solved their problem yesterday and they replied,
"What was up?"
"someone had swapped the gel tank around so I ran the gel in the wrong direction"
They crossed the beams :)
I told them not to worry, I tried to run a DNA gel with water rather than running buffer once and my solution when the loading dye refused to move was to crank up the voltage. I almost managed to set fire to water...
EDIT: Only noticed I'd titled this "Wal of shame". Oh, the irony.