Dire Necessity

We need a new series of hand signals for car drivers. Now that we no longer indicate direction by sticking our left hand out the window, we need to come up with some universally recognized signals that indicate:

• Thank you for letting me merge in front of you
• I am so stupid for cutting you off! I'm so sorry!

I am partial to the idea of punching myself in the head when I make a mistake in driving; it exhibits penitence, frustration with my error as well as an obvious understanding that I am the one responsible.

But when it comes to the thank-you gesture, I can't think of anything good. The fairly common "wave in the rear view mirror" feels too casual, too insufficiently grateful.

As to expressing frustation, I would also like a gesture that exhibits a feeling of "You were very stupid there, I am very mad, but I acknowledge that you might not have meant to be so careless." Honking or flipping someone off is too mean if it is a genuine oversight on their part; they drive on feeling very hurt and offended.

Ideas? Followed by, How on earth do you make a signal universally recognized?