"I am serious."
I would put it as bISaghlaHbe', qar'a'. Since we've never seen qar'a' used as a name, it doesn't work so well, but finding a joke like that would be great. There is a Klingonist who goes by the name pagh. So every time someone asks a question like, janglaH 'Iv "Who can answer?" and someone says pagh "No one," we all turn to look at pagh for an answer.