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2.
To give, to share something with someone.
Slap me up with some of that dirty burger, you monkey. (whilst at McDonalds.)
by Trevor H. December 01, 2003
 
1.
The act of striking one's flaccid penis against their own lower abdomen, in order to create a resonating 'clonking' sound.

It is absolutely essential that the penis is flaccid. The softer the penis, the louder and deeper the 'clonk'.

Having lots of excess foreskin can also have an advantage as it adds a 'whipping' noise to the 'clonk'.

If the tip of the flaccid penis can reach the naval, then it creates a beautiful, deep 'bonk' sound.
Once the slap up has been fully mastered, the 'clonk', 'whip' and 'bonk' sounds can all be heard with one well timed crack of the penis.
Some slap up's can be heard for miles around, and is said to be part of a mating call used by people in certain parts of the world.
Once again it is essential that the penis is flaccid. Striking a hard penis against the lower abdomen can cause the penis blood vessels to burst, bruising, internal bleeding, and even death.
Pete: 'Hey Dave, can you hear that resonating clonking sound coming from over there?'
Dave: 'Yeah I think its someone having a slap up.'
Pete: 'What makes you think that?'
Dave: 'I can smell it.'
by Charlieballbag May 14, 2014