I need to think about this too... slash staples done as gen are great fun... and you can dare me back, although I don't have much time meself and I'm a very slow writer... but crack is crack... I think I've got it, get ready 'cause this is a biggie:

A gen hypothermia/share body heat story, must include the line "this is not what it looks like" (worded as you prefer) and a third canon character that draws wrong conclusions (can be corrected or not)