I loved the old Unison public service union one. Cartoon ant carrying a leaf walks across the screen, only to find its path blocked by a dopey-looking polar bear. "Excuse me! Excuse me!" it squeaks, but the bear takes no notice.
Ant marches off the way it entered and comes back with a friend. "Excuse me! Excuse me!" they squeak. Polar bear looks around but fails to see them and doesn't move. Both ants march off again.
The third time an entire army of ants march on. "GET OUT OF THE WAY!!" they yell in - wait for it - unison (geddit?) making the polar bear scamper over the horizon, and leaving the path clear for the ants. Made me laugh anyway, but then it doesn't take much. :O)