The reindeer sweater (gag) is a tough call—thanks, as usual, to the 1970s and, probably, Ron "How the Grinch Stole Christmas" Howard. Technically, though, you should never color-coordinate or otherwise theme what you wear on any national holiday. Fuck 'em, including Franklin D. Roosevelt, the man responsible for making amateur hand-turkeys a national pastime. (On other things, he was not so wrong.) Besides, it usually looks terrible.
If you must wear a reindeer sweater, the one marginally acceptable holiday-themed garment, get the right one. That is the secret—must be a secret, 'cause no one gets it. You want the right material—the woolier, the more natural, the better. You want a simple design—no bedazzling, and as few reindeer as possible. And you want a good fit; a close fit. No sagging, no bagging. It shouldn't be hard to find, now that Medium fits like Small again.
That's it; it's not difficult—though, apparently, it is. And the toughest problem of all is one we can't help you with: the fact that, if you wear this thing before, say, the first week in January, you're going to look like a tool. Really, do yourself a favor and leave the reindeer sweater for next month, when it'll be reallycold in California. It might even freeze. Or rain.And it won't be some holiday.