Bounced up to say hello, looked directly into my eyes and then started blushing.
Close runners up are;
Picking me up for a event after a few weeks' dating where I was stressing about having to wear something formal and doing makeup, etc - when I opened the door, he did the jaw dropping thing, followed immediately by a huge grin and 'oh, my God, you look amazing!'.
Overheard having a conversation with the cat. The cat was replying, making it obvious that they had regular chats when I was still asleep.