If “Happy Christmas” (2014) is a Christmas movie then all y’all need to shut the hell up about saying “Die Hard” isn’t a Christmas movie. “Happy Christmas” happens to take place at Christmas, but it’s really just a character study about a ne’er-do-well layabout sibling that brings joy to a mundane home when not almost burning it down. Anna Kendrick is the ne’er-do-well and Melanie Lynskey (priceless in “Two and a Half Men”) is the sister-in-law who could use something/someone to rouse her from a post-partum funk. Every generation has these types of middling dramedies. This one’s for the millennials.