If the choice is really that bad, spoil your paper by writing something on it. I was at a count that had "SXXX MXXX is shagging MXXX JXXX", i.e. a local councillor and the local Labour MP. All the council tellers pissed themselves when they saw that and the returning officer had to show it to all the other candidates to ensure it was a spoilt paper.
Turned out it was true as well...
The other one that works is spoiling it by putting your own politics - anti-war, anti-capitalist or a local campaign - on the paper. This won't raise such a smile but it does worry the hell out of Labourites.