‘There’s a demon inside me,” Stu (Ed Helms) confesses to his best friend, Phil (Bradley Cooper), near the end of the redundant, repellent, and occasionally amusing The Hangover: Part II. Normally a mild-mannered, easily emasculated dentist, Stu has just survived yet another alcohol-fueled, memory-erasing pre-wedding bacchanal. Last time (that is, in 2009’s The Hangover), he and his “wolfpack” — as the bearded man-child Alan (Zach Galifianakis) dubs their group of friends — were in Las Vegas, where they misplaced the groom whose nuptials they were celebrating, while somehow acquiring a prostitute’s baby, a fey Asian gangster, and Mike Tyson’s pet …