Probably the prototypical example of this is when Homer is spraying bottle after bottle of lighter fluid onto the barbeque. After 25 seconds of pouring (like 3 bottles later) he carefully moves a match close to the grill and…
a modest size flame starts up the charcoals normally.
Of course, we all expect the thing to blow up in Homer’s face (which IMO would have been funny too, in a slapstick-Homer-football-in-the-groin sort of way), but the writers know we are anticipating this and pull a switcheroo and make that the joke.
There’s another one I can’t think of, but I saw recently. Maybe had something to do with Homer falling out of a window and Barney was driving. Well whatever.
Can you think of any? Seems like a recurring theme, and they are usually good for a chuckle.