The Nay Sayer will never agree with you about anything. He always knows better. It does not matter what you have said, the answer is "no, not this one, that one".
You may have suggested a Vietnamese restaurant in town - you have proposed the wrong one. The Other Vietnamese restaurant is more authentic, the food is tastier, the decor more agreeable, and the prices more reasonable.
You may have mentioned that Mr. X seems to be doing a good job - the answer is no, Mr. X is lacking in such and such qualities and it is Mr. Y who is doing the better job.
You may have thought that A was a pretty good movie - there are at least seventeen major flaws in it which he can readily identify, and you should really see B, it was a much better film.
The weather may seem to be perfectly miserable, cold, windy and wet, but no, no, saith the Nay Sayer, this is exactly the kind of weather he prefers, which is why he moved to San Francisco in the first place. Any other kind of weather is for bad-tempered people who do not really deserve to live.
There is no subject the Nay Sayer is not familiar with. You may taunt him with suggestions that Polish Lap Dancing has it all over the Serbian variety, and he will regale you with quite graphic descriptions which should surely change your mind.
You cannot get the better of the Nay Sayer. Even if you tell him that you did see movie B, as he suggested, and it really was much better than movie A, you find he will have changed his mind, and now movie A is the genuine masterpiece, whereas B is purely trash.
At length you will surrender to the infinite wisdom of the Nay Sayer. He talks louder and longer than anyone else, with great effect. After several lunches with this man, you will find you have lost your appetite for commenting on anything ever again.