This is a question I get asked frequently. Everyone can be hypnotised. You just have to find the right way of accessing whatever trance state they utilise easily.
All of us experience trance like states every day - in front of the TV, arriving at our freeway turnoff after a long drive and realising we were sort of switched off, daydreaming in some other place. These are the starting points for accessing the subconscious so that we can add suggestions to the, now, open mind.
At the beginning of the show I let people know know that there are three types of people that can't be hypnotised - kids under 8 or so because they are so open anyway , people that are drunk or stoned because they can't focus on my voice and those of low intelligence (again because they can't focus).
You can check this out yourself when you come to my next show. And who know, you might...be hypnotised. :)