Or he's just that easily flustered and awkward around people. Especially when being teased. Go with that--simpler explanation (even if less kind to Amy's ego).

"I'm not going to fall, or drop you, or anything like that." Mumbled under his breath, exasperation more than clear now. "Yes. On three." Letting her count though, and then doing the simplest thing and closing his eyes, on 3.