Heard this from a guy who was camping out in my room in yeshiva (using the yeshiva as a free hotel and restaurant for a couple of days at a time while he had dates in the neighborhood). I believed it at first but now I have my doubts.
He’s on a date with a girl and offers her a drink a few times but she declines each time. Finally she says, “Can I have a drink now?”. He says, “Sure, can I get you a Sprite?”, but she wants a Coke so he gets her a Coke.
Before she starts drinking she says a whole hinneni mechaven… that she’s not drinking the Coke for tayvos olam haze, but rather to give her koach to serve the Ribono Shel Olam even better. She then makes a Bracha and takes a drink.
She then explains that it is assur to drink Sprite since it is tayvos olam haze, but Coke on the other had has caffeine to give her strength to serve Hashem, so it’s muttar.
He’s sitting there totally bewildered not knowing what to do. Finally he says, “Are you having a good time here?” to which she answers, “Yes, why?”. “I’m going to leave now so if you’re having a good time you can stay but if you want a ride home you’re welcome to come with me.”
The reason why I later doubted the facts of the story is that my sister told me the exact same story was a Purim play in her seminary (with the exception being that the girl in the play brought along a kizais book).
He also told me another story (similar to Ms. Ex-vegetarians-ex http://www.theyeshivaworld.com/coffeeroom/topic/funny-shidduch-stories/page/11#post-57443 ) but I’ll have to post it later when I have more time.