Ugh, coming up with something "cool" under time constraints, while someone is sitting there and watching my every move, is not exactly a realistic gauge of anything. One of the reasons the hiring process is so broken for so many is that they fail to take in to account the nervousness and pressure the candidate will invariably be feeling. Speaking as someone who has done many interviews, questions like this always make me cringe. Sitting there in a suit, sweating and angling for a job, isn't really the best time for me to come up with something "cool."
i meant this more in the sense of "what's a piece of code you've seen(or written) that made you excited and made you think 'wow that's really clever!'" It shouldn't necessarily be something earth shattering, could be very simple, just something you genuinely liked. I personally believe enthusiasm (including intellectual curiosity) is the most important quality somebody can have in the workplace.
If your problem with the question is trying to think of a response that the interviewer would want to hear, then you aren't approaching the question correctly and/or neither is the interviewer.
