Yup, I do the same twitch thing. I think the twitch/similar is better then vocal outbursts though, those are much more embarrassing and is more likely to force you to explain yourself.
Two nights about while eating dinner w/family in front of the tv I remembered back to something earlier in the day. I suddenly made a deep "Grrr" sound as I mentally punished myself for not handling a situation with a stranger more smoothly. Luckily I was only surrounded by my family at the time, those who looked at me strangely with raised eyebrows. I just said "It's nothing" to blow it off.
You know if we didn't have to fear these sorts of 'slips' and didn't have to bottle our emotions, etc. up I doubt this would happen, would it?