A Hanoi high five is derivative from the term used in the film 'Tropic Thunder', but has evolved into a sexual move.

A Hanoi high five is where your partner is on the bottom preferably , when they're are at the point of orgasm (liberating the south) you land a bomb/grenade to the dome. There are variations of the finishing move, i.e throwing them out of your house/flat/village/country , ejaculating or ask them to concede victory.

This move can also be used on the back foot, an example below.
The first example would be in a forced sexual situation where you are not the aggressor.
1. He mounted me and when he was about to liberate the south, Bam Hanoi High five.

Another example for emergency situations

1. You are making love, she decides to tell you at the point of liberation "hey you want to meet my parents", Hanoi high five, a perfect gesture to decline that meet.
by _GreenEggs&Ham_ June 15, 2019
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The act of raising your hand as to give a high five but instead a grenade or any other explosive is thrown. Hanoi coined from the vietnamese, who had a fondness for doing this in the Vietnam War.
Used in Tropic Thunder.
A: We're being backed into a corner! We're surrounded!
B: It's time to hanoi high five these fuckers.
by Lensty October 11, 2009
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