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
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 2, 2003
Slap up

adjective BRITISH informal
(of a meal or celebration) large and sumptuous. First rate.
We went for a slap up meal on our wedding anniversary.
by broken spoke May 9, 2018
The act of hitting or slapping someone abrubtly, for saying something foolish.
"That was crazy.....don't make me have to slap up up somebody"
by Nafurtat August 19, 2015

1) the way of describing a senior member of staff negatively critiquing a piece of work, even though effort or partial effort was put onto it.
2) the way of a member of management unjustifiably “destroying” / “going-to-town” on a piece of work in front of colleagues to make them feel superior.

In both examples this leaves you deflated and wondering why you bothered. A few hours of job searching usually ensues.

Not to be confused with ‘bussing’ where a similar level colleague purposely discredits your work due to lack of effort on their part so it gets ‘slapped up’ to draw attention away from them.
"Stephen just threw me under the bus"
1. I don’t know man, my manager is gonna absolutely slap up my work.

2. Kathy is absolutely destroying my work, slapping it up all over the place.

Employee 1: how did the meeting go?
Employee 2: *double slap hand gesture*
Employee 1: ah shittt
by Topgun89 February 11, 2020
An event where non people, i.e artists and transgender folk, gather to strip naked and slap each others bodies whilst wearing false nails. Towards the end of the event, the tide turns from innocent naked slapping into an intense sexual affair where the slap of pelvic thrust against chafed buttocks gives it the name 'Briggsy Slap Up'
A group of funny folk were spotted catching the next mini bus to the Briggsy Slap Up
by Rubber Sheath September 19, 2006