It is a long-standing meme in exercise culture that Monday is "chest" (and maybe biceps? or was it triceps?) day in gyms all around the world. There is a degree of truth to this, which is part of what makes it funny.
The other subtle insinuation and layer of humour in the meme is that many of the people who show up to the gym for International Chest Day will not show up on any other day.
What we miss while we are busy judging the subjects of this joke is that there is something valuable in there: routine.
Our routines are the foundations for our habits; good and bad, productive and useless, just and unjust alike.
Regarding your exercise goals, is your routine helping you or hurting you?
Ps. If you don't like crowds, stay away from the bench press area today. ;-)