On machines sliding around, if the show is somewhere with concrete it is *incredibly* easy to slide these machines (it's like being on ice sometimes). Out here PPE and Pin-A-GoGo are on concrete floors and I always wind up accidentally sliding a machine or two half a foot, when doing the same physical move on carpet/hardwood would have only jiggled the machine. I'm just saying, sometimes things look more physical and worse on those floors than they actually are. But if that is too much, definitely set the tilt bob so it does the talking for you.
On 4-player machine hogs: I also will step up and ask if I can join in (I offer/ask for most games I step up to anyways). If they refuse, it's up to you to decide if they are far enough along in their game to push it to the next level (or if there is a line...how long said line is...etc.). Some of these people also just suck at pinball, so they need those 3 other player slots to compensate.
If they are done and reload up another 4-player game, it's definitely time for the next level: which is find the staff and tell them about the rude fuck.
Paying for admission to a show doesn't make someone special enough to hog a popular game. Especially since everyone else in the room paid the same price to get in. The only time you're entitled to hog a game is when it is sitting inside your house.