Flair up 

To put on a user flair on a subreddit, an integral part of r/politicalcompassmemes' culture.

Generally, user flairs are used to categorise the users on a subreddit, like the personality typology subreddits, the alignment chart subreddits, political subreddits, any reason to categorise people. Or, you could make the flairs editable, as an extension of one's username on the subreddit.

Obtaining a flair is what to 'flair up' means.

Unflaired: Hello, I'm new to this subreddit.
Authleft: Good, now flair up, comrade.

Flair up by typologer June 23, 2020

Flair up 

When you go crazy or stupid , unexpected stuipedness

Your standing in line to get your caramel none fat almond milk decaf macchiato And all of a sudden you start dancing to the song that’s playing in the coffee shop
Your best friend: wow that was a flair up

Flair up by User3456789 April 8, 2019

Fair Up

An expression of support or encouragement. Used for footy teams, and often used to goad willing friends into illegal or stupid activities.

Australian slang.

#1: Fair up the Titans!

#2 (while on the back of a ute doing more than 100km/h): Fair up 'im Davo! Feed it!

#3 (while convincing mates to get fuck eyed): Fair up the beers aye.

Fair Up by kingofspin March 12, 2020