my one's not that good - I was once at a club and couldn't find my coat where i thought i'd left it. I saw some guy wearing my coat and went up to him and asked him if he was wearing my coat. he denied but i didn't believe him and persisted on and on until he eventually got annoyed but sort of convinced me he was telling the truth and i dropped the questionning. Later on I found my coat where i'd left it. I still sometimes see him around town.
Anyway, some of you lot must have some stories of these types of hilarious misunderstandings that are sitcom-worthy, being that you're all a bit socially awkward an all.