Yes! This has happened before; it's not a restaurant, though... I was in a store that sold some imported Japanese goods, and they were playing anime music and stuff, so I didn't really recognize any at first, but then... BAM! Ayu comes on! I screeched the minute I heard it, and some people stopped to stare, lol. The song was Depend on you, so I was able to sing along to myself quietly when I walked through the store XD The girl at the check out counter asked me if I liked Ayumi, and I said yes, so she showed me all of the Ayu goods they had that I didn't even notice before, lol. It was a great day, because I was able to get A Complete ~all singles~
So, no, you're not the only person who gets excited XD I freaked out and spazzed so much that day...XD