I saw him in the West End production of Noel Coward's "Design for Living". I wasn't familiar with the play at all, and I remember it being such a great, eye-opening experience of how amazing theatre could be. The next day I went to the book store (remember those?) and bought many volumes of Noel Coward's plays.
I chose the play because it had "Mouse" in it, and I'm so glad I did. He was excellent in it.