In celebration of the occasion, we're having a threesome party! (Get your mind out of the gutter.) If you're a couple, bring an extra single person. If you¹re a single, find two to accompany you - but you MUST come in multiples of three! No costume required, no thematic soundtrack is planned, but you gotta bring that odd person. Or that odd number of people. Or that odd number of odd people. Anyway, you get the idea.
BONUS: bring someone single and we'll get 'em drunk for free! We'll wash away those post-Valentines blues. And who knows, maybe some of the single folk will meet other single folk. Or perhaps this won't be just a joke of a theme for this party. Regardless, you'll have no excuse to go home alone.