Feeling the burning in your bosom? You could just say you've been "preparing for your future duties as a wife/husband"...getting a little beforehand experience ya know? So you're ready... Or how about "Mind your own business you little creep." That should do it.
Buffin the muffin (for the ladies) slaying the one eyed dragon Polishing the rocket baiting the master cylinder flogging the dolphin slammin the salami churning the butter beating the bacon winding the crank frosting the pastry cleaning the cavern (again for the ladies) spanking the frank greasing the crankshaft