On flights to las, there are frequently groups traveling together (generally one of them is getting married and the others are there for the bachelor party), and after they have had several rounds of drinks, they can get boisterous--when I was flying DL I noticed this more than AA, since I am now usually in fc and with the few seats available one would not have a group in fc--but on dl in economy there were instances where they were tipping the fa (in addition to the price of the drinks) and so were probably drinking many more rounds than they should have.