once, there was a group of us on a bus, late at night, and i really needed the toilet, but the driver wouldn't let us have a piss stop. i waited as long as i could and eventually used a plastic 2 litre bottle i'd just finished drinking from (and managed to fill it, more or less). i put the lid back on so that it wouldn't spill and shortly afterwards a friend on the seat behind me, who had been sleeping, awoke and said that he was thirsty. he saw my bottle and asked me for a drink, so i passed the bottle back to him. as he took it in his hand, he complained that it was warm and i pointed out that i hadn't thought to bring the fridge with me. anyway, he removed the lid but everyone burst out laughing and stopped him just in time
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i have other bus-related stories that didn't end so well (one of them involves fire!).