One last bit of requesting advice though: If I wanted to break or steal a PC's weapon, how would I best go about doing it? I want to sort of kick the table leg out from a PC or two and make them think or act differently.
I highly suggest talking with your player(s) (outside the game) about this before you do it in the game. Explain your reasoning and they may be fine with it. But, every player I have DMed for would quit playing if I just did something like this to them with no warning. People dislike being told they can not do something and playing their characters how they built them to be played is top of that list for many of us. Yet, if tell them what you want to do (and why) and give them the option of going along with it or not they will likely go along with it.
As for the metagaming problem: If they said, "I'm going to charge through the line of enemy clerics so as to draw their attacks away from my friends!" Rather than talk about attacks of opportunity and such would you that better? If so then tell them that you'd rather hear the characters thoughts on why he would do the action rather than the meta comments and that the characters have no concept of game mechanics.
Talking to the players is always the key.