Straight: Charlie and Diana are Happily Married, and have a fairly stable relationship, in comparison to AliceandBob, who are only on-again-off-again dating, and have a Slap-Slap-Kiss relationship. Charlie and Diana are supporting characters, Alice and Bob are the leads.
Exaggerated: Charlie and Diana had Love at First Sight, have been married for twenty years, and never fight, ever. Alice and Bob are only Friends with Benefits, and they fight every day, and when they do, it's like World War III.
Downplayed: Charlie and Diana get into less fights than Alice and Bob, but are by no means a perfect couple.
Charlie and Diana's personalities compliment each other, while Alice and Bob's clash.
Charlie and Diana have been married for a long time, so they know what they're doing, unlike Alice and Bob, who have only been together a few months.
Inverted: The main characters have a more stable relationship than the supporting characters.