schadenfunin
Schadenfunin: laughing at other's private jokes/stories.
After hearing the man at the next table apologize 'for last night' and the girl he was sitting with said sadly, "don't worry, it happens to all guys." The man tapped a bumper out on the table as if punctuating a joke. I laughed so hard that milk came out my nose. I pretended that I was choking rather than admit to schadenfunin.