Details, please?
We were in the YC on the Mera and were surprised to see guests in pajamas in the dining room at breakfast, and men with ballcaps on at dinner. But the cruiseline allowed this (much to my chagrin). What this "very very very poor behavior"? No. But certainly not the standard I'd ideally like to see. (You wanna wear jammies? Order room service or eat by the pool, but not the YC dining room would be my preference.)
If you want to see really bad behavior, jump on a 3 night booze cruise out of FL, not the YC on MSC (in my opinion).