Yep, some of them are classic.
I've done two things like this, one in an internal GCSE mock and the other for my GCSE science:
1) Internal GCSE mock. An ICT question was "Name 4 principles of the data protection act". I went on to list "Thou Shalt not kill", "Honour thy mother and father" etc etc.
2) GCSE science. I honestly forgotten how to spell the world "plane" (as in aeroplane - it was question about why is static electricity dangerous etc). So, after spending 2 minutes trying to figure out how to spell it ("playen", "plain", "playn" etc) I ended up putting "big aluminium flying machine". I wasn't trying to be funny with the examiner, because it was my actual GCSE and I didn't want to lose 2-3 marks due to forgetting how to spell "plane".