Ever since an intern referred to George's patient as McBurney in the series premiere, the good doctors at Grey Sloan Memorial Hospital have made a habit of adding "Mc" to words and sentences. The lingo is intriguing as it normally brings some sense of humor to serious or gloomy situations.
The most commonly used "Mc" labels on the show are McDreamy and McSteamy, referring to Derek Shepherd and Mark Sloan, respectively. However, the use of those "Mc" labels has been minimal ever since both characters were killed off. Luckily, there are plenty of other McSomethings in Grey's Anatomy.
McRebound
Thanks to her hospital roaming privileges, Addison returns to Seattle Grace in Season 4's "Piece Of My Heart" to perform surgery. She realizes a lot has changed since she was last there. Most importantly, Derek has parted ways with Meredith (much to the dismay of fans) and is now seeing the scrub nurse Rose.
In the OR, Addison inquires about Derek's new girlfriend, referring to her as the unlucky McRebound. She isn't aware that she is gossiping about the scrub nurse handing her the instrument. When Addison discovers Rose is in the room, an awkward moment follows. She is right about the rebound reference, though, since Derek soon leaves Rose and goes back to Meredith.
McBastard
Derek and Meredith hook up for the first time at Emerald City Bar, aka Joe's, a meeting that results in a one-night stand. Meredith is unaware that Derek works at Seattle Grace too and when she finds out, she begins avoiding him. However, he doesn't give up on her. His persistence eventually pays off and Meredith agrees to date him.
Things get complicated when Derek's estranged wife Addison arrives at Seattle Grace for work purposes. Realizing that Derek is still married breaks Meredith's heart. While venting to Cristina, she refers to Derek as McBastard, and rightfully so.
McHardcore
Cardiothoracic surgeon Erica Hahn always presents herself as an extremely confident woman during her stint at Seattle Grace. Her work is at the top of her priority list, though her fling with Callie Torres later makes a claim for her attention.
Callie and the patients are the only people who see Hahn's softer side; the rest of her colleagues get the tough treatment. Hahn is quick to speak her mind, too, whenever she is uncomfortable with something. Her personality soon earns her the nickname McHardcore. Sadly, she quits after the Izzie and Denny incident.
McFrickin' Code of Silence
Callie isn't too happy after finding out that Meredith told George that Callie slept with Mark Sloan. She confronts Meredith in the changing room and calls her out for not keeping the McFrickin' Code of Silence.
Callie is right to be angry. She reminds Meredith that she witnessed her having sex with Derek and chose to keep quiet about it. She also pulled Meredith's undergarments from the bulletin board to save her from embarrassment. Given how much Callie had covered for Meredith, the favor ought to have been returned.
McDreamy
This is the "Mc" label that fans love the most. Even people who don't follow the show have probably heard about it. And there's nothing complex about its origin.
As soon as Cristina finds out that her friend Meredith is seeing Derek, she nicknames him McDreamy. She figures he is the man of any woman's dreams, thanks to his good looks and charming personality. The name sticks, with staff around the hospital occasionally referring to Derek as McDreamy.
McWidow
Cristina hasn't appeared in the series since she left for Switzerland but in Season 16's "Let's All Go to the Bar," she sends Meredith a rather interesting text message. And it's about a man.
She asks Meredith if she got the package she sent and Meredith lets her know she didn't. Cristina then clarifies that the package is a human, the new Head Of Pediatric Surgery, Dr. Cormac Hayes. The surgeon used to work at Cristina's current hospital in Switzerland. Cristina thus lets Meredith know that Hayes is McWidow, implying that she has a chance with him.
McDreary
The question "what if?" is asked in Season 8's "If/Then." In the episode, an alternate reality world is explored, in which Derek is McDreary instead of McDreamy. He is still married to Addison and is unaware of her affair with Mark.
Meredith, on the other hand, is engaged to Alex. Her mother Ellis Grey is still alive and married to Richard Webber. She is also the head of the hospital. What's worse is that McDreary is less successful. He lacks the drive that Derek has and isn't as loved. McDreary indeed.
McSteamy
When Mark Sloan first comes to the hospital, everyone is intrigued by him. George, Cristina, Alex, and Izzie begin gossiping about him as they watch him suturing his own face. George asks if that's the guy Addison was cheating with and everyone agrees that she can't really be blamed because Mark is too good-looking.
Meredith joins them and the group tries to figure out a nickname for Mark. After ruling out "McSexy" and "McYummy," they settle on McSteamy. The name sticks for the remainder of Mark's time on the series.
McHot
During a conversation with George and Alex, Cristina begins wondering why Derek and Mark are so intrigued by Addison. She can't understand what they see in her. Alex bluntly tells her that Addison is McHot. George agrees.
But as attractive as Addison is, Derek makes the right decision for ultimately choosing Meredith. Addison's infidelity incident had broken him and their marriage was clearly over.
McVet
Meredith finds herself in a dilemma when the veterinarian Finn Dandridge begins hitting on her. Meredith first meets Finn when her dog becomes sick.
The Grey's Anatomy protagonist finds herself in a dilemma because she likes both Finn and Derek. She asks Cristina for advice about McVet and Cristina advises her against dating him because she doesn't like vets. When Derek finds out about Finn, he breaks up with Meredith. Meredith then realizes she wants to be with Derek and breaks off with Finn.