In my opinion slapstick works best when it’s something unrealistic happening in a realistic setting.

Cartoon slapstick doesn’t really work because the situation is already unrealistic, so stuff like that would be expected and blend in too much with the cartoon setting.

Live action slapstick on the other hand, can be knee-slap worthy because of something unrealistic happening in a realistic setting.

(I remember a year ago I said slapstick wasn’t funny at all. Well my opinion has certainly changed.)