Gurney - I used to work in a library so it was a fairly routine occurence.. however - book shops in general have me needing the loo, and W H Smiths is my favourite place for 'cruising and losing'... browsing around the shelves, dropping little silent but violent 'messages' around them. The aim is to 'drop' one, move round the shelf unseen and then come back around when some poor unsuspecting schmo has taken your place. You then sniff audibly and glare at the person now standing in the cloud you left behind. The trick is to not 'lose it' and giggle whilst trying to glare the other person into blushing.

It's not clever, it's not funny (for them) but it's cheered up many a boring afternoon for me!

LTS