I love it. Clown fiesta is creativity at its finest. It makes me laugh every time I see it. I don't know where it came from, or even how long it's been a thing on these boards, but I think we need more phrases like this.
It's not just boards. It's been a term used on streams, reddit, youtube, etc.
I think it's a shout caster thing. Car full of clowns, ford fiesta, clown fiesta.
Every time I see that term it makes think of doing a one for all with 
as the champ on both teams
If you laugh every time you see a clown fiesta you should play tank supports, or ADC if you wanna see them in Black & White.
I prefer the term 'cluster F**' cause of all the possibilities of what it could actually mean.
It's a thing all over the league community https://www.youtube.com/watch?v=OwZA-RZI2wU there's a dyrus video as an example
It's horrible
A clown fiesta is usually when all normal rules in a game get tossed out the window and pure madness occurs.
Examples: Yogg-Saron or Mayor Noggenfogger in Hearthstone. Extreme non-meta picks in LoL. (Blitzcrank Top, Yasuo ADC, etc.) Team full of RNG heroes in Dota 2. (Chaos Knight, Ogre Magi, etc.)
Clown fiestas are EXTREMELY AMUSING when the CLOWN FIESTA becomes the NORM. For example, Ziggs Bottom Lane.
