Exploited: Bob goads Charlie into shoving him specifically so Alice will beat him up.
Defied: "Seriously, Bob, fight your own battles."
Discussed: "Don't mess with Bob. Alice will kick your ass."
Conversed: "Uh-oh, someone pushed Bob while Alice is nearby. The fight scene's about to start."
Deconstructed: Bob feels emasculated by Alice's constant defending of him. Their relationship suffers.
Reconstructed: Bob and Alice have a talk about her defending him and Alice only steps in to help only when he is clearly in over his head.
Played For Laughs: Bob is a shameless coward who cringes behind Alice at the slightest hint of danger, to the disgust of friends and enemies alike.
Played For Drama:
Alice's protectiveness towards Bob is due to the fact that he is often bullied by others which severely damages his self-esteem. It motivates her to beat the crap out of anyone who bullies him while she's within proximity. Even when she's dating him.