-A person who is over the top or being completely ridiculous
-Someone who has pushed you over the edge and become quite a problem
1."Wow she just stole my seat, what A Mandy":
2. Hey look at that girl wearing a teal puffy jacket what A Mandy 3. "Would you like to go on a date with me to Wendy's" Fuck no you are such A Mandy
UK origin. Named after the French girl's name Mathilde, and generally used to express a combination of amusement and embarrassment (sometime with a dose of incompetence), much like the world view's the French.
Doing a Maddy is most commonly used when you have done something that is embarrassing to you, but amusing to others unintentionally. It is often used as a pre-emptive response to the ridicule you will anyway be in for and admit defeat before it even begins.
Laura: "I did a Maddy this morning..."
Lisa: "Really? What happened?"
Laura: "I overslept and tried to wash my hands with toothpaste"
To piss oneself in public -- usually, but not always, as a result of too much drinking at one's defence party.
Person 1: "Hey, did you see Jane pull a Manda last night?"
Person 2: "Seriously?! She pissed herself at her defence party?!"
Person 1: "Yeah! I guess incontinence really is a symptom of too much grad school."
Person 2: "That and being a total derp."
Person 1: "Oh yeah, Jane is a total derposaurus, just like Manderp."
Person 2: "lololol, Manda is a total derpinatrix."