Megadeth played the Annexet in Stockholm, Sweden on July 31 and there was a bit of an unplanned interlude between songs.
Someone who had a little too much to drink started heckling frontman Dave Mustaine, who playfully gave the person the finger and tried to carry on with the show. The person kept going, at which point Mustaine began to tell them to "shut up" with increasing frustration in his voice. Eventually it seems like the person stopped, but not before Mustaine quipped "See, that’s what happens when cousins fuck." Ouch!
Maybe if the person threw something on stage it would've been more acceptable? They were dissatisfied with the show, after all. In all seriousness though, getting drunk at shows is fine – just don't be a dick when you're too lit. I guess that also goes for every other situation in which you're intoxicated, too.