GM style is completely different from person to person. I like my players to have some degree of background, an idea of their character's appearance, and some other specifics down pat. One of my newer players hated that, so he left the game. No skin off my nose. I like to try to bounce between players, interrupting their long diatribes of actions in order to allow everyone a chance to play. No one has ever been upset with that. I prefer the characters in my games to be more realistic, so I try not to allow combinations of things that are only viable due to loopholes or unclear aspects of the rules. And I try to stick to the "1 minute" rule, wherein if I come across something that I can't figure out in 1 minute, I'll just make something up on the fly to keep the game moving.
All that is to say that my style isn't for everyone, just as many of the GMs I've played with haven't really been for me. In fact, the whole reason I started GMing in the first place was because way back when I played D&D. My DM had me take a herring to a tree, while chanting "ni." Now, I'm as big a fan of Monty Python as the next nerd - but to me that was too much in the silly direction. I knew I wanted my games to be more... gamey, but also to stay fun. It took me years to refine my style, understanding what to look for in players before they did something I didn't like. As a result, I don't really have to "smack down" my players - I simply see what is coming and prevent it from coming up.
When I do demo games though, I let the freak flag fly. Players can be as crazy as they want to be, because it's not a campaign and the characters' actions won't have any repercussions. What I think this means is that I have a varied style of GMing, and I can adapt to several situations. Not every GM can do that. For a long time, I couldn't do that.
When I think of "smacking down" a player, I think of a GM hitting someone with something impossible to defeat, without giving the player or character any chance of warning. For instance, let's say there is a door with a lock that the characters have no chance of overcoming. The characters should still be able to kick in the door, blow it up, hit it with spells... something. If I say that this is an invincible door and they should have picked up Lockpicking when I told them to... that's childish as hell on my part. The GM should allow the players to have a chance, even if it's not always the ideal. In that example, let the characters kick in the door or whatnot, but it sounds an alarm. It makes the rest of the run harder, but it doesn't stop the game because I wanted to be right.
So to me, that's what "smacking down" a player would be. If a GM has more than 2 years of experience and is still doing that kind of thing, they're a crap GM.