"Knights of Cydonia" by Muse. When we eat lunch I usually play music and he really seems to love this song. We do air guitar and hand motions and all kinds of crazy stuff while we sing along.
Edited to add: No, this is not soft-core pr0n. They're both wearing pants and it's just one tiny section from an awesome video featuring futuristic women on unicorns, cowboys with laser guns, and random kung-fu fighting moves.