In the cinema it has to be The Rugrats Movie and some god awful tripe called "Star Kid". Both times I was dragged to the cinema against my will because other family members wanted to see them (I think I was 12 with both films, so I had no say).
Outside of the cinema, it's either Ben-Hur, Spartacus or Gladiator, all 3 have nearly sent me to sleep and I've never seen either of them in their entirety because they bored me so much.