used to have 2 funnels, one orange one for oil, one white one for water, sadly I put the orange one in the washer bottle by mistake and filled it with oil. Next step go to breakers yard and buy a new washer bottle, as trust me the oil never seems to come out and squirt oily water on the windscreen does not end well!
Had a VW 1974 VW Beetle whilst I was at Uni… driving home for the weekend down the M6 and multiple red lights popped up on the dash… pulled over and put half a litre of oil in (it did use a bit oil now and again)… got back in…lights had gone off… carried on… all great…
20 mins later, red lights on the dash again… “ah, I can’t have put enough in…” - poured the rest of the oil I had in…
Started her up, accelerated down the slip road to join the M6 and realised there was a James Bond style smoke trail behind me for about 200 yards… had to pull over as there’s no way anyone else would have been able to see a thing.
Phoned AA man who diagnosed a faulty alternator… had to get towed home.
Lol Dave
Ditto 
Might have been if there was enough front wheel arch space. Not good noises. 
Put some wheel arch spats on my first Mini, all went fine until I found I had no rear lights anymore …
I had drilled stright through the rear loom that was close to the wheel arch behind the rear seat …
Same Mini, put some spacers on the rear for the new Wolfrace wheels I had bought … used the version with longer studs and did the job proper I thought … took for a test drive with some mates and had a huge tank slapper at speed on the local test track … found all wheel nuts loose … I didnt pull the studs all the way through and seat them out … that was a close one …
Had the gearbox rebuilt with Jubu 3rd 4th and straight cut final drive. But was ridiculously noisy on the road. Thought not hearing of anyone stripping the final drive, it’s usually 3rd or 4th. Had the box rebuilt again to put the standard final drive back in. Two track days later 5 teeth ripped out of the final drive at Anglesey and a long flatbed ride home. Another gearbox rebuilt to put a semi helical Jubu in. Expensive all round. BTW the semi helical wasn’t available on the first rebuilt.
Motto, try to do it right and do it once even if it is more expensive.
Not long ago I was renewing the brakes on our old Passat.
It was late evening when I got to the final step, brake bleeding.
Hooked everything up as usual. I’m using about 1bar of pressure from my compressor.
BOOM!!!
Everything, and I mean everything, was sprayed in brake fluid and the reservoir shattered as I charged it with the full 8bars from the compressor.
Need to make another one of those step-by-step checklists and add “reduce pressure”.
/Michael
I can totally sympathise with that, you only do that sort of thing once! 
I didn’t think it would be long before a pressurised brake bleeding mishap would surface. I’ve taken one off before and not thought to release the pressure, then it’s time to push the vehicle outside and rinse it off. 
My car upgrade/repair mistakes over the years would be able to fill a best seller.
I was very please with the neat job I made when I fitted a map reading light on the door of my Mini.
Worked and didn’t fall off until I closed the door and car filled with smoke.
Stupid place for a door hinge. 