If you're really in love with someone then every single day should be Valentine's Day. You should be over the moon with the person you're with and do everything you can to pull romantic gestures out of nowhere to make them happy.
With that being said though, there are some expectations for Valentine's Day that people have: you're expected to have something magical planned that'll get your SO feeling all warm and fuzzy inside.
The thing about romance though, is that there are several ways of going about it. Humor, in many instances, can be very, very sexy. But there's a fine line between funny and tone deaf, and telling a joke on Valentine's Day might just ruin the whole romantic ambiance you're trying to set up. What you're looking for is playful, not offensive.