The Waitress is the unnamed love interest of Charlie Kelly in the sitcom It's Always Sunny in Philadelphia.
The Waitress went to school with the gang, but none of them can remember her name for some reason. She's a recovering alcoholic, but after being pressured into drinking by Dee, she falls off the wagon and becomes much more belligerent. The Waitress has also experimented with ecstacy, which makes her more friendly and outgoing.
Despite her sour attitude towards Charlie and Dee, The Waitress is actually a fairly decent person. She's a member of the Big Sisters program and often shows a more caring side whenever she thinks something is wrong with Charlie.
Charlie has been stalking The Waitress long before the series began. His friends always comment on how creepy it is, yet Charlie still persists. The Waitress has taken out numerous restraining orders in the hope that he'll take the hint, but to no avail.
In the Season 4 finale, Charlie reveals that he's written a stage play and he invites The Waitress to attend, promising to leave her alone if she does. At the end of the play, Charlie breaks into song and proposes to The Waitress, who bluntly says "No". She then reminds Charlie that she held up her end of the bargain and he has to stop stalking her, but Charlie goes back on his promise and says he'll see her tomorrow.
It is later revealed after Charlie starts seeing another woman that his stalking was actually protecting The Waitress from an alarmingly high crime rate in her area. When Charlie reveals that he was only dating another woman to make The Waitress jealous, she allows Charlie to stalk her once again, knowing that he was nowhere near as dangerous as the people coming after her.
The Waitress has a crush on Charlie's friend Dennis. Dennis doesn't seem too interested in her, being more in love with himself than ordinary women. The two have dated occasionally and have even slpet together, but Dennis still doesn't know her real name. The Waitress' fixation on Dennis parallels Charlie's fixation on her, as she's willing to be manipulate events so that Dennis will notice her.
When The Waitress thought that Dennis had made a sex-tape of them, she enlists in Mac's help to retrieve it. Mac agrees on the condition that he can sleep with her, as he wants to spite Charlie for destroying one of his videos. Charlie later tells Mac that he wasn't destroying his video, but the sex tape Dennis made out of anger.
When Dee told The Waitress that Dennis was sleeping around while they were dating, she decides to get revenge. Dee told The Waitress to start sleeping around as well and see if Dennis likes it. All of this was a scheme of Charlie's into getting with The Waitress. In the end, The Waitress sleeps with Dennis and Dee's father Frank. When the gang find out, they are all thoroughly mortified. All Charlie can do is shed a tear.