A fist bump was an action where two people bump the knuckles on their fists together. Graham O'Brien tried to do so 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)
Mickey Smith and the Tenth Doctor occasionally bumped fists. (TV: Doomsday, Journey's End)