What were they thinking? I mean really, what?

When you set out to make a thing (and I use the word "thing" advisedly) like Four Christmases (2008), how does the thinking go? Do you start out with, "Well, I'm going to tell the studio I'm making a cheesy slapstick holiday movie like Lampoon Vacation or Home Alone but then I'll slip some relationship stuff in when they're not looking." And then do you get about 19 days into the schedule and realize you'll have no time for the relationship stuff, so you just skip it?

Or do you start with the nice relationship stuff and the evil studio (and in this case, it's New Line, and they ARE evil) makes you shoot a bunch of crap about falling off the roof while installing the satellite dish and 9-year-olds streaking and (wait for it--god, this is so-o-o-o-o funny) babies emitting fake projectile vomiting. Who the heck is this supposed to amuse?

Or is it unfair to blame any of the filmmakers for what they wound up with because, no matter what the script said, Vince Vaughn wouldn't shut up with his endless irritating unfunny adlibbing? (And how come Reese Witherspoon has to be reed-thin, while Vince Vaughn goes on getting fatter and fatter? Is he going to start auditioning for those Orson Welles parts?)