At most dances, there's a big grindfest in the middle of the dance floor, where all the girls are back to back in a big circle grinding asses together, while all the guys make a bigger circle around them, jumping up and down and acting like frat guys.

Anatidaephobia is defined as a pervasive, irrational fear that one is being watched by a duck. The anatidaephobic individual fears that no matter where they are or what they are doing, a duck watches.

Anatidaephobia is derived from the Greek word "anatidae", meaning ducks, geese or swans and "phobos" meaning fear.

Having a party where everyone is grinding. Guys on guys, girls on girls, guys on girls, doesn't matter. Everyone is fucking grinding til the break of fucking dawn

A dance where everyone on the floor (or off the floor) is grinding

a high school dance

people rubbing asses together.

Grindfest, comes from Scandinavian/Norwegian word "Fest", and English word grind

Fest means to celebrate a occasion.
Grind in online terms means to repeat an action to get something, money to loot.
When you combine this words, it becomes Grindfest, as in we're celebration and occasion and earning money and/ -or loot