Christmas hands you mistletoe — an actual socially sanctioned flirting mechanism — plus naughty lists, stockings and unwrapping, so these lines have more infrastructure than any other holiday's. Office parties and December nights out are the season; the closer to the 25th, the more forgiving the audience.
The sweet ones suit cards and texts. The naughty-list ones suit the third drink onwards.
December is the most target-rich month in the calendar: office parties, markets, family gatherings with plus-one questions, and an actual plant whose entire cultural function is licensed kissing. The naughty-list material peaks at parties; the sweet material belongs in cards and texts, where it reads as charm rather than a move. By Boxing Day the whole genre hibernates, so spend it while the lights are up.
The adjacent seasons have their own ammunition — New Year's for the week after, Santa lines for the costume-committed, and the full holiday collection for the rest of the year.
