What's your favorite use of ironic or 'inappropriate' music in a film (diegetic or non-diegetic)?

What's your favorite use of ironic or 'inappropriate' music in a film (Diegetic or non-diegetic)?

Using 'out of place' songs can make a scene or moment feel very memorable and stick in our minds.

I'll kick it off with one of my favorites: The use of Enya - Orinoco Flow in David Fincher's The Girl with the Dragon Tattoo.