I know there's already 2 threads on this but they died 3 years ago so I'll repost it and hope it becomes more popular then those :)
Mine is when I (alone) sat on this 5 hour train from Stockholm to Gothenburg. I was drinking a can of soda, this was the start of the trip, and suddenly made a LOUD burp that the whole wagon could hear and probably the ones next to it. It became quiet and everyone stared (or glared) at me, some giggled but most of the looks I got were more like 'son, i'm going to kill you'. Anyways, I got all blushed and tried to sink down as low as I could but this pair came up to me and started yelling about how inappropriate I had behaved just then and why I should not do this and that, just like parents scolding a child would. I had to live for 5 hours with the stares of everyone onboard...
Now tell your story :)