I love this scene from
The Birdcage. It's not a great movie, but I remember that he played the (pardon the pun) straight man, while Nathan Lane played the neurotic, over-the-top comedic one. Except in this one moment where he cut loose and showed that nobody could over-the-top like Robin Williams.
ETA: good grief; I forgot the link:
https://www.youtube.com/watch?v=H5TQ4GF8rNI