[Under normal circumstances, Chekov tries to keep himself in line and behave like a respectable and responsible adult.
These are not normal circumstances and he doesn't feel like being respectable or responsible.
No part of the new prison is safe from an enthusiastic and possibly-slightly-tipsy Russian. There are caves to explore and rides to go on and games to play! Food needs to be eaten! Everyone needs to be told that their favorite things were actually invented in Russia! He has several years' worth of not acting like a child to make up for and he's going to do it all at once!]