cockslapping

Swaffelen (or zwaffelen, similar to "dick-slap") is to hit one's soft or semi-erect penis — often repeatedly — against an object or another person's body. Swaffelen is Dutch and was named as the word of the year in the Netherlands and Belgium in 2008.
The act of swaffelen often takes place in the form of teasing, crude humor, or a degrading context, but it can also be a sexual act. When the act is practiced on a person, it is often the person's cheek that is hit with the flaccid or semi-hard penis. Similar terms exist in other languages.

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