Although you did your best to arrive swiftly with complete surprise, the Angevin garrison at Alençon rallies quickly, and your first assault is repelled with loss. The Angevins mock you, and call you the "son of that tanner's daughter" (referring to your mother, Harlette, and her common origins father). Not only have they insulted your legitimacy, they have insulted your cherished mother.
You control your temper, and decide it is time to swallow your pride and ask king Henry for help.
You attack in anger and lead the assault yourself from the top of a scaling ladder.
Control your temper. It seems obvious that you can't take the place with them prepared for you. So throw a few catapult bombs, start a few fires: ignore the cretins: then when it is obvious that no amount of mouthy Angevins can get the best of you, withdraw back to the siege of Domfront with your honor more or less intact. Prestige is everything, if that is all that you have.