Ranma and Ukyou? If Ukyou could get Ranma in her bed, the first thing she wants to hear are wedding bells.

Ranma and Shampoo? Unless bells have something to do with her culture's wedding ceremony that comment doesn't work. Besides, she would be ecstatic to marry Ranma.

Ranma and Kodachi? Assuming you could get Ranma into Kodachi's bed without being drugged, you'd still have to consider that Kodachi wants to marry Ranma. If her chasing Ranma was all a game and not attempts to marry him, then she'd turn this little morning after into a game as well.

Ranma and Nabiki or Kasumi?  Soun would have them in front of an altar immediately upon suspicion. Nodoka and Genma would help.

Ranma and Ryoga? Ryoga would commit suicide first.
 
Ranma and Taro? Sick, wrong, and Taro would kill Ranma first.

Obviously not the right answer. Try Again.