On the usenet newsgroup alt.fan.pratchett (and very possibly other groups too) a tradition sprung up of expressing one's admiration for the wit, erudition or personality of another poster -- particularly a female poster -- by proposing marriage to them. Many posters to the group, as a result, have a disturbingly long list of 'afpfiance(e)s".
Over time, this being usenet after all, "Will you marry me?" became abbreviated to "WYMM?". There was much discussion on the froup whether such a cavalier approach should even be dignified with a response, let alone an acceptance, but eventually a formula reply evolved - "HMMHYG?" (translation is left as an exercise for the reader -- though I will respond to /msgs if you are really stumped).