Valentines for my best friend which is soon to be my girlfriend, any ideas?

Basically, I am sort of in love with my bestfriend, which she knows since we are in this 'flirtationship', and i want to make this valentines a favorite memory of hers as we are soon to separate after year 11 ( 4 months left!!). I thought of making this valentines more hilarious than romantic because believe me, we love our sense of humor. Any ideas of what to do for example a prank ? :D
Thanks

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