oh yes cocked up once, in a rush one day to make a tip time but had to get fuel, so pulled into the unmanned station chucked my card into the machine and just glanced at the pump I had stopped next to for the number on the side, it had been snowing heavy and the front of the pump was covered in snow, grabbed the nozzle and started filling, put about 100 ltrs in when I saw the red sign under the snow, yep 100 ltrs of red in the tank, quickly moved to the next pump and put another 400 ltrs of good stuff in, bit embarrassed when I had to phone the boss to tell him 
Bloke at my old place filled a 7.5t full of petrol. He only realised when the fuel card got rejected, and he ended up paying for it with his own cash… Then got charged off the boss for recovery, drainage, PLUS the diesel that was already in the tank.
i remember a few weeks ago talking to another driver and he was telling me and another fellow about this driver who spoke to him saying how its taking a long time to fill the ad blue tank up,he replied it should not do if he put the ad blue in the correct tank and not the diesel tank,and no i did not catch if he was an agency or not[the ad blue driver]
in the garage the drivers top up water on the coach in the mornings when they leave
we had just got 12 new Volvo’s in and the oil and water caps was next to each other 
he had put 1 water can of coolant in the engine oil and driven out the garage
he was called up and told to bring it back
we did a few oil changed and its been fine since
mind you we called him Oil for the rest of this time at the company
Fantastic stories, loved the ‘fuellish’ joke 
I did actually put 4 star into my diesel car once, very early am, forgotten to fuel up the night before my weekly commute from SE14 to Manchester (yep, serving out my remaining notice period in my old job) came off the 25 at Potters Bar looking for petrol pre 6am and by this time suddenly busting for a wee. Spotted a Jet, zoomed in grabbed the ‘black’ pipe without looking, filled it up, paid and rain in and begged to use the staff loo (which fortunately she let me). Made it as far as the next junc and managed to coast off at the slip (uphill!) and died at the top. Gutted when recovery towed me all the way back into west London to have the tank drained. As you can imagine I was a bit late by the time I made it up to M’cr. No biggie that way round though, car didn’t care.
Just remembered, I actually had two mobile phones with me, neither of which was working as I was swapping networks - my old one had switched my no off and the new one hadn’t turned it on yet! 
Fortunately someone stopped to check on me within 10 mins so borrowed his.
Had a driver get off the boat in St Malo and pull into the Total garage just down the road (the tiny one!!) Put in 200 litres of 4 star and only realised his mistake when his fuel card was rejected 
Fortunately he had the sense not to move the truck…saved our costs as we only had to drain and refill the tank but the garage were going ballistic with him sat on the pumps. Fortunately he played the stupid Englishman card well that day!
This is going back a really long way.
About 1961, I think. I had a full time job selling ice cream in S Wales. In the morning we had a routine, like most places, that included fuelling up, checking fluids and the LPG tank for the generator.
On a hot summer’s day, I was asked to take a new student out on his first day to show him the ropes. I drove the van to the pump, opened the bonnet to dip the oil, and told him to fill it up, while I went in to get my float etc. When I came out, I asked him how much. “Half a gallon,” he said.
I assumed that the pump had just cut off (as they do) and went round to fill it properly. He watched me open the filer and said, “I think I might have done it wrong.”
Turned out that he had put the petrol into the oil filler cap and filled it to the brim. No sales for me that day - Doh!
Slight tangent but, way back i was parked on a garage forecourt, saw a lady poor gallon of oil into mini engine, was suprised when she went back in and came out with another gallon.
Thought i would poke my nose at this point, turns out she was going to keep pouring till she could see the oil in the cam cover!