I usually don't give advice on strategy. After all, what do I know, and who am I that anyone should listen to me? But we've all had to deal with this particular problem and I've given it quite a bit of thought over time.
I would agree with Ronaldadio, be patient and pick your spots. Obviously, if someone is making constant and repeated pre-flop shoves, common sense
tells you they can't have it every time.
It's important to pay attention. When someone does call them, what kind of
hands are they turning over?
Are they shoving with bigger hands like K-Q, A-J, or even something like Q-10? Or are they getting them all-in with any Ace or any pair? Or maybe they are shoving with anything that seems even slightly palyable like Q-8 or J-9? The kind of hands they are playing are going to determine the range that you should be calling them with.
Some players will shove from certain positions with any two cards. Rather than make a standard sized raise to steal the blinds from late position, they will shove all-in to prevent you from playing back at them. Some players use all-in bets to take advantage of perceived weakness at the table to steal pots. For instance, when two or three players limp into a pot in front of them, it becomes very tempting to shove all-in and try to take it down. The reasoning being that if nobody has a hand strong enough to raise with, then they definitely aren't gonna be strong enough to call an all-in bet. In fact, all-in bets early in a tourney (especially S&Gs) are specific tactic that some players use to influence the way others at the table are playing. It intimidates them and makes them unwilling to raise out of fear that this guy is going to go all-in over the top of them. The lack of a raise allows others to limp into the pot, thus creating the opportunity to pick up a nice little pot with, you guessed it, an all-in bet.
Don't assume these are all just donkeys and maniacs. Some are. Some have no real poker skill and are just there to gamble. These guys are looking to chip up early so they can have a stack to sit on and wait for pairs and Aces to shove with. For others, this a strategy designed to manipulate and take advantage of other players. They're likely to switch up once they lose a chunk of their stack. Either way it's important to shut them down early. The bigger their stack is, the more aggressive they are likely to play. More chips, more donk!
I can't stress enough how important it is to be patient and pay attention. Dealing with these guys is always dangerous. The best hand doesn't always win, and the worst players tend to get the luckiest. With time and experience you'll gain the skill and confidence to deal with them. But remember Fred, you knew the job was dangerous when you took it.
For someone who didn't have much to say, I sure said alot, didn't I?