Interruption. I always trained my servers not to interrupt a conversation and wait for the customer to acknowledge them, and to walk away if they sense the conversation is deeper than the deep dish pie they hope to serve them.
Upselling, upselling, upselling. I always try to strike conversations with servers to get the inside scoop on those questions, then I ask, "how many times out of ten do you sell a drink, appetizer or dessert the customer wasn't planning on. 1 -2 of ten is the usual answer, but they are not sure out of those if they would have wanted them with out the upsell.
Ignoring you if your busy. I go right to the manager and explain the art of service to him or her and that his server is ruining my and my guests dining experience. For some things, especially manners, I have no patience. It takes takes two seconds to say "I'll be right there" with a smile.
One last one. When the server brings an order to the table they know is wrong, not properly prepared or mis-timed so the temperature is not right, and they know it. Grrrr...