The problem with naming least favorite holidays is that there's so many random days that people get off work or school, and that's literally all it is, nobody actually celebrates them.  Labor day being both simultaneously my favorite and least favorite of the uncelebrated holidays because of the irony aspect.  However, in regards to holidays that I personally have witnessed being celebrated, I'd actually have to say Valentine's Day.  That's not to say I hate it or in any way dislike it, I just don't find it to be my cup of tea.  That wasn't always the case, when I was younger my family would make homemade, specialized valentines for each other, and our parents would give us each a big ol' bag of mixed valentine's day-style candy.  Now it's just kinda eh, whatever.  I've never been interested in the romance aspect of it at all, so that would probably be why.

Question for the next poster, what is your favorite board game and why?  I love board games, and like to think I have a pretty solid collection, but the best collections are the ones that grow.  So if you're into board games as well, what would also be a board game you really enjoy that you don't think many people know about?