This is an area of game I'm consciously working on and can do it away from the table. Having moved to Boston in the last year the level of sharking and poor sportsmanship is at a pretty high mark. Where I came from, in Hoboken, NJ, players were much more cordial and about playing the game well and leaving it at that.
In our HLT a couple weekends ago our opponents were cheering loudly for our players to scratch, yelling nice shot after an easy shot where our player left himself hooked behind another ball. They had players walking around the table when our player was on the 8 ball and just about anything they could think of to get under our skin they did. And they did it successfully. As much as I tried to convince our team to ignore it, it got under their skin and we played unintelligent and mechanically poor pool and lost. I never got to shoot being saved for a possible sudden death rack and would have loved to have tested my nerves in that environment...
To me, the reality is that people can pretty much say or do whatever they want or feel like. Yes, it may make them complete douches, but at least you know what type of person they are. To let that person beat you who spends more time in learning to intimidate an opponent than he/she does in learning the game of pool is a disservice to the game itself. These games/matches need to be won and if you're game is at all affected by their actions, then it's an area that needs to be improved upon...
Ten years ago I was known to get rattled by the juggling and jangling of the quarters by an opponent when I was on the 8 ball. Whenever I played with friends I'd have them rattle quarters on my 8 ball shots just to get me over choking in that scenario. If you're thinking about what a douchey moron your opponent is, you're not thinking about the shot...
Although, I totally sympathize with your frustrations over annoying players like that. Playing in an environment where that type of thing doesn't exist is sure pleasant, but beating the piss out of those guys who are asses is even more enjoyable.