Forgot the filter tube in my cooler a couple times. That involves scooping hot mash into a bucket to get at the inside of the spigot. I've tried to do it blind with oven mitts in a garbage bag, but the wire mesh opening is too flexible, you really need to be able to see it to coax it on.
The worst however, was when I was setting up my taps on my bar. I have a 6 tap tower on the bar on the main floor, with kegs in a fridge in the basement below it. I had gotten one tap hooked up just in time to show off for a party, and it worked flawlessly. Two weeks later I hooked up another keg. Connected the beer line, headed upstairs. I DID remember to check to make sure the tap was closed first. Pour a pint, worked fine, stand there looking at the tap.
Drip.
From the back of the tap.
Hmm... I wipe it, and lean closer to see where it comes out.
Drip. From the next tap.
At this point I decided to disconnect the beer and tighten some things. Go downstairs, open the fridge, and beer is SHOOTING out and spraying all over the inside of the fridge. Just everywhere. It was coming out of my homemade trunk line, it had backed up all the way back around the outsides of the beer lines. Got soaked trying to pull the line off the keg.
What I ended up figuring out was that the O-rings on the built-in shanks on the tower were broken. By some miracle, the first tap I hooked up was the ONLY one with intact seals. ALL the rest were broken, and since the first tap worked I thought I had gotten everything right.
I had to pull my trunk line all the way back out of the wall/floor, deconstruct it and replace all the insulating foam and plastic wrap that was soaked in beer, reassemble and replace. And wrapping/zip tying all the beer line is NOT a fun or easy task.