How to get revenge on my Uncle?

Last week my family went to my grandma's house for a birthday party. My Uncle who is 38 years old is super cool. In the middle of the whole family eating desert he comes up behind me and tickled me. Well I laughed and screamed. It was so embarring. I want to get him back. This Sunday for Father's Day we are going to his house for a BBQ. I want to tickle him back. He is ticklish on his feet and armpits. What is the best way to tickle him? I want to get him back good.