A-Level Chemistry Practical Exam
This was a fairly standard titration experiment, titrating some substance (I forget which) into potassium permanganate solution. Permanganate is a deep purple/brown liquid which stains everything it touches. In a rush to get everything set up, I filled the burette (a long thin glass tube that's very difficult to clean) with permanganate instead of the solution I was meant to use as titrant. That of course wouldn't be dumb enough for a post here. With no chance of cleaning it out myself, I sheepishly caught the attention of an invigilator and asked for a clean burette. Luckily, he managed to find one quite quickly and I was back on track, a bit delayed and very embarrassed but otherwise none the worse for the accident.

Relieved, I pressed on and filled my shiny new burette to the top with potassium permanganate.
( JimM, Mon 31 Dec 2007, 12:47, 4 replies)

... LOL U R FUNNIEZ

( Bats, Mon 31 Dec 2007, 13:28, closed)

Oh my
I would have just DIED.

I have no idea what your talking about
( Adamsky, Mon 31 Dec 2007, 18:38, closed)

Sadly, I do know what you're talking about.
And yes, such things make you feel like an absolute twit.

My favorite? I went to measure the current in a circuit during a test and blew the fuse on the power supply three times before I remembered that you put the ammeter in series with the circuit, not across it like a voltmeter...

That's why I went into mechanical engineering instead of electrical.
( The Resident Loon Not a demographic. Do not measure., Mon 31 Dec 2007, 19:00, closed)

:)
This reminds me of the following 'Pure Ignorance' QOTW answer by Soapy Norris, which is possibly my favourite answer of all time:

'The shame, the shame
This happened not to any chav, blonde, tourist, American or anything of the sort but to little old me. Not saying something stupid, more doing.

I had to plumb in a new washing machine a couple of years back. I undid the compete U-bend assembly beneath the kitchen sink, which meant that the plughole now drained into thin air. I emptied the skanky old water from the washing machine hoses & U-bend into a bucket, then poured it.... into the sink.

Water everywhere, all over me, the floor and everything in the cupboard beneath the sink. So, cursing myself for my sheer idiocy, I duly set about mopping up as best I could and wrung the remains into the bucket.

Which I poured into the sink.'

b3ta.com/questions/ignorance/post21212
( The Helpful Bear, Mon 31 Dec 2007, 19:15, closed)