Fist bump

A fist bump was an action where two people bumped the knuckles on their fists together.

Instances
Mickey Smith and the Tenth Doctor occasionally bumped fists as a show of friendship. (TV: Doomsday, Journey's End)

Finn the Human and Jake the Dog once fist bumped, shouting "It's battle time!". (WC: New Adventures Await!)

Graham O'Brien tried to bump fists with Ryan Sinclair, but the latter kept refusing to do so. (TV: Rosa, The Tsuranga Conundrum) However, he eventually returned the gesture. (TV: The Battle of Ranskoor Av Kolos)