Bob had issues with his wife sleeping around on him. He probably felt like he had no control over his life so the jelly donut incident was just the straw that broke the camel's back.
Carlton is lonely and old and his nephew is a salesman for crying out loud.
Sandy is a successful lawyer who is hung up on a guy from her past. She cannot seem to disconnect herself from the past for whatever reason so she definately gets my vote.
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But seriously, let's talk about jocularity.