I can't remember which one it's in (I think it might be the one which ends with the firework factory exploding in Hong Kong), but there's the scene where Clouseau has to book 'a room' for the night and the hotelier can't understand his accent.
I did hear a story about this scene, but it might be just fictional. Apparently, the actor playing the hotelier was a genuine smoker and so smoked for real on his pipe during the take. Someone is supposed to have spiked the tobacco with weed, so as he and Sellers fluffed their lines etc, both became progressively more stoned in the cloud of smoke

.
I can't recall the titles, but here are some of my other fave moments:
Sellers posing as a cleaner with an overly-powerful vacuum cleaner and an escaped parrot (guess what happens

)
Clouseau posing as an old one-legged sea captain complete with inflatable parrot - it keeps deflating. Utterly stupid scene, but somehow funny.
The repeated failed attempts by assassins to kill Clouseau. The two killers who shoot each other in the toilet cubicles when Sellers drops the loo roll on the floor.
Clousea accidentally setting fire to Dreyfuss office.
Dreyfuss, about to be released from the psychiatric hospital, discovers Clouseau dressed in drag in his wardrobe - the 'Peek a boo' line is a cracker.
Clouseau jumps in his car to chase the crooks and the car promptly falls apart 50 yards down the road. He calmly suggests to Cato that the car could ' do with a service'.
Years ago when I lived for a short while in West Hampstead, Bert Kwouk was my neighbour

.