Attitude (often motto) present in many elitist or successful groups of people especially at wealthy, elite private schools, expensive highly-ranked universities, and among yuppies. Basically means that one works hard at school or their job while they also party on the weekends (or weekdays as well, depending on how far they take it).
Stupid because it basically provides an excuse for mindless partying directing one's life without any space for taking anything seriously in the world.
Sometimes leads to side effects like alcoholism. Usually outgrown as one gets older.
Ivy league student: Hey look at me I'M SO DRUNK HAHAHA
Old high school friend: Wow you weren't like this in high school. As I recall you were really studious and nerdy...
Ivy league student: WHAT CAN I SAY WORK HARD PLAY HARD