"Acting the fool" or "telling someone off." Making your displeasure known loudly, because someone didn't (for example) pay you what he or she promised.
To convince yourself that your crush is indeed liking you back when in fact it's uncertain or just all in your head.
"Yeah, he's still clowning over that girl that rejected him weeks ago because she liked his post"
"God I'm clowning so hard over this guy but he's sending mixed signals, idk what to think anymore"
Acting like a "funny" character online but failing so hard to do so that people are wondering if you are being serious and in the processreally retarded or plain stupid or really succesfull in doing so.
Clowning is wondering if someone is being stupid or playing a character:
I am wondering if Anunki is Clowing, i'm really not sure. His posts are so weird, nobody knows what he is on.
The art of beating anybody in anything. Clowning is the term one wishes to use when expressing the utmost dominance. Can be used in a similar fashion as words such as "pwning".