Margaret Smith is a recurring character in Regular Show and is former love interest of Mordecai and Eileen's best friend. Unlike Mordecai, who is a bluejay, Margaret is a "robnal" (robin/cardinal hybrid). Margaret was unaware of Mordecai's feelings for her and considered him a friend. She works at the coffee shop where Mordecai and Rigby like to go. A running gag in the show would be for Mordecai to try and do something to impress her, only to find she has a new boyfriend, usually someone muscular and scary. After the episode "Camping Can Be Cool", she stopped seeing guys because she accepted everyone she's dated were jerks and goes camping with Mordecai, Rigby, and Eileen. After that episode, she was starting to become aware of Mordecai's feelings for her and after the episode, "Butt Dial", she kept a song Mordecai accidentally voicemailed to her.
Their relationship almost becomes official in the episode, "Bad Kiss". In the episode, Mordecai tries to find his wallet in the car and Margaret tries to help. They end up looking each other in the eyes and have their first kiss. Margaret pushes him away though since his breath was bad. Mordecai runs to his room, despairing that he ruined his first kiss with Margaret. Rigby gives Mordecai a time machine he bought for 15 dollars that ends up working and makes sure the Mordecai in the past doesn't kiss Margaret. He ties up past Mordecai and Rigby sends him to the past and the time machine (now two cuz Rigby went back in time and bought another one. Mordecai and Margaret see each other and Margaret almost kisses Mordecai but he finds the wallet and walks out and makes everyone "Mordeshakes." Time will tell if they have a new first kiss.
In "Do or Diaper", Muscle Man mocks Mordecai for not kissing Margaret and bets that if Mordecai can't kiss her by the end of the week, Mordecai would wear a diaper. Mordecai accepts the bet, hoping it would give him courage to finally kiss Margaret. Marget finds out about the bet, and while she forgives him, she tells him to enjoy the diaper.
In "Picking up Margaret", Margaret needs a ride to the airport and Mordecai offeers to drive her there. Because of the events in "Do or Diaper", she stays suspicious but agrees to it. Mordecai borrows Benson's car but makes a cell-phone hating gang called the Wickets mad at him causing them to chae Mordecai and Margaret. Mordecai is able to defeat the gang and get Margaret safe to the airport. Margaret thanks him and admits he's a great friend. Before she leaves, she kisses Mordecai, making him very happy.
In "Meteor Moves", Rigby tells Mordecai that Margaret's kiss was a goodbye kiss and he is still in the "Friend Zone." Eileen tells everyone about a meteor shower and invites everyone to go. Mordecai believes he can finally kiss Margaret during the shower but still stays nervous. Rigby finally gets fed and tells Mordecai he's sick of never following through. Mordecai in his nervous state, says he and Margaret are friends. Mordecai and Margaret are then literally trapped in the "Friend Zone," a Phantom Zone like area and a moonlike creature kown as the Guardian of the Friend Zone tells Mordecai that is punishment for waiting too long to kiss Margaret. Mordecai promises to kiss her if it means escape for both of them and the creature gives the two another chance. Mordecai finally kisses Margaret and the two finally begin a romantic relationship.
In "Family BBQ", Mordecai, now Margaret's boyfriend, is invited to her family's BBQ. Mordecai learns that Margaet's dad never shakes hands with any boy Margaret brings home. Mordecai heads to the BBQ and meets Margaret's family and meets Margaret's father, Frank Smith, who is the traffic reporter for the local news. Mordecai offers his hand in a handshake, but is denied. Mordecai is told Frank will shake hands with anyone who beats him in cannonballing. As the contest goes on, Frank goes into his helicopter, which Mordecai goes into. When they both fall, Frank confesses he's worried that one of Margaret's boyfriends would take her away from him. Mordecai assures him that Margaret thinks he's a good dad. Frank and Mordecai finally shake hands as they plummet to the ground and ends up saving their lives.