I can't name just one above all dear, I had many of them with my ex boyfriend. Also it's hard for me to choose between the ones with me as the tickler and me as the ticklee. One of the best was the first time I tied him up, we started out playing with ice and flavored massage oil and ended up tickling later. It was really good because it was the first time either of us had done something like this and we were so like 'wow' hehe.
The best time with me as the ticklee was one morning when he decided he wanted to tie me up, and I decided I wouldn't mind being tied up as well. For some reason, either I was extra ticklish or he was extra merciless that morning... maybe both 😀