tricky one! I would probably say "leave it!".. since it's your thesis, and you should be able to put a little of your personality into it.

BUT! Is a thesis going to be archived for anyone later to read? Maybe even reflect the quality of education people receive at your uni? Should that be the case, maybe the lecturer, even though he loves you, will look at it through more conservative eyes due to social unacceptance of any sort of humour when it comes to academic writing.

I'd leave it, just to make a point of *owning* my thesis... but be prepared for any critisism ;) Good luck!