The middle finger. It has to be that.

Flash the hazards twice, also works as a thank you for letting me merge in or whatever, it’s pretty common in the UK.

I have gone to using a single hazard flash when people are in front of me as well instead of flashing high beams(reserved as the head tap equivalent for cars) because I hate when people blind me at night trying to thank me… high beams are way brighter than they used to be.

Brake check them

raise your hand?

had a brain glitch on a roundabout, nearly forgot to break for a passing car.

Like this 🖕

Hand up, and bow head.

I roll down the window and do the Sorry/ThankYou Wave. 👋

Especially if they DIDN'T honk.

I have a huge purple dildo. I just start beating myself about the head and shoulders.

Sorry? Hell naw. Double down. Make it their fault. Get even more mad than them. Brandish your gun. Then brandish your second gun. Fire a warning shot towards their vehicle. Finish your beer in case you need to get out of the car. Challenge other driver to fisticuffs. Lose. Go home and explain to wife why you lost another fight. Get sad. Go to bar. Get really drunk. Pass out on stoop of the Wayne County Building. Miss work for the 3rd time this month. Get fired. Get kicked out of house by wife. Move into bachelor apartment. No artwork on walls. Only Kroger brand bread, condiments, and cheese slices in fridge. See kids every other weekend. Start going to AA meetings on a whim. Find new job. Hit the gym. Find new hobbies. Meet new girlfriend. Come to terms with faults and find peace through meditation and mindfulness. Experience growth. Drive to work one day. Accidentally cut a guy off. Double down...

I think the fact that there isn't a good way I think escalates a lot of otherwise defusable road rage situations.

I usually just honk “SORRY” in Morse code.

(Edit: real answer) For most acknowledgements, I double-tap a light — beams, brakes, or hazards depending on current lighting conditions and relative position of other driver — because most things I would say to them are two beats long:

• “Thank you”
• ”Sorry”
• “My bad”
• ”Go on”
• ”Nice drift”
• ”You drunk?”

Just hit their car slightly with yours. You know, a love tap, to show them love and appreciation. Then show them your extended middle finger, signifying that you are standing with them in solidarity of thinking you’ve made a mistake. If you have a weapon with you, you can hold it up and show them to indicate that you are aware you could be perceived as a threat, but are making the effort to indicate that you aren’t.

Bow head down slightly, lift your hand slightly like a weak wave, show a little humility in your eyes if they meet.

Can't go wrong with the classic 🖕. 

I flash my hazards for a sec. I also use that to say thank you.

I usually wave at them as though I think they're a friend of mine just saying hello.

I wave the back of my hand with all my fingers up except my thumb, index, ring, and pinky

I find that rolling over and showing my belly, while impractical, is reliably effective at diffusing these situations.

I've seen people put both hands up a little above the steering wheel and that was probably the clearest way I've seen.

I pretend to shoot myself in the temple.
Then I put the gun back in the glove box.

Look ashamed and maybe do a single flash of my hazards.

Usually I point at them aggressively to get their attention and then start miming Gluck glucking to show them how much of a dumb whore I am.

I don't think it's working though, usually they just flip me off and look real angry.

Honk louder to assert dominance.

Back of the hand high and visible through the rear window, fingers and thumb slightly apart to reduce the chances of them thinking your giving them the middle finger (or two fingers in the UK).