I have mellowed out quite a bit over the 22+ years I've been running our poolroom. I have just come to accept many things I didn't used to, as I can't afford to run off customers, and I realize we just don't have the kind of poolroom that has knowledgeable players. A very large percentage our our customers are families with kids and even adult players who have played very little, if ever. They don't really know better what is and what isn't cool to do in a poolroom, and what kind of actions can cause harm to the table/cloth. I feel it is my job to inform them of these things, but it must be handled very delicately, as a negative experience may result in them never coming back.
It's obviously much harder to bite my tongue just after I've spent $450 per table having our tables re-covered. Two things I absolutely will not tolerate - players who dig under the ball as their only clue as to how to execute a jump shot, and recreational players who elevate their cues to show off their attempt at a masse shot, when they are absolutely clueless as to what they are doing.
In either case, I will immediately approach the table and the player, and discreetly, but firmly, let them know we do not allow that here, that it will damage the cloth on the tables, and to please refrain from doing it. If it is a kid and they are with their parents, I will approach the parent directly to explain, and not reprimand their child right in front of them. Most people are very nice and understanding, as long as you treat them with respect and you don't make a scene and embarrass them.
However, you just can't please everybody. Recently, when we last had our tables recovered, a man and his teenage son who come in occasionally were wrapping up their play. In the process of getting the balls back in the tray. I looked down and the son was gouging under the object balls with his cue, trying to get them to jump up and land in the tray. After seeing he wasn't just going to do it a few times, but was continuing to do it numerous times until he had them all in the tray, which clearly would have done major damage to our new cloth, I flickered the pool table light to get their attention from the bar, and shook my head and simply said you can't do that. When he got to the counter with the balls to check out, the man was so upset feeling that I had completely embarrassed his son and and he imformed me that he would never be coming back. I tried to explain to him what his son was doing could damage the cloth, and his comment was that his son was doing it very easily and carefully, in order to not damage the cloth. Some people just don't get it. Anyway, I got my point across, but I did apologize to him if my actions had embarrassed his son, and they do still come in.