|Although this article is based on canonical information, the actual name of this subject is conjectural.|
The Neanderthals were a group of four college men who were placed under a temporary spell from a potion that was tainting the beer that they were drinking. The potion turned anyone who drank it excessively into a Neanderthal. The potion was brewed by Jack, the owner of the pub that they were drinking at, as an act of revenge for being mistreated by college students for twenty years.
Xander, who had recently obtained a job as a bartender, attempted to flirt with a sorority girl named Paula. Paula responded cheerfully to Xander, but their conversation was interrupted by Colm. Colm immediately tried to dismiss Xander and talk to Paula himself, but when Xander refused to go away, Colm immediately insulted Xander's intelligence by purposefully acting smarter than him. Colm then asked that Xander serve him a pitcher of Black Frost (beer), to which Xander initially refused to serve him unless he could provide an ID. Before he could obtain the ID, Jack, the bar owner, told Xander to "just give him the beer," to which Xander, although annoyed, obliged.
Later, Buffy, still suffering from the sadness of a breakup with Parker, accidentally bumps into Roy. She is invited to join the four men for a few drinks. She accepts this offer, hoping to drown her sorrows.
The nights pass as the four continue to drink together and descend further and further into a state of drunken stupidity, to the point where they can only form incomplete simple phrases such as "You stupid," and "Where girl go?" Xander, in an effort to protect Buffy decides to cut her off. The four guys remain and continue to drink, although they are disgruntled with the fact that Buffy left.
The four men continue to drink past closing time to the point where they can hardly form a coherent thought. Hunt and Kip get into a slap fight, Roy struggles to take his shirt off, and Colm goes to use the bathroom. Xander informs them that it is time to pay up and go home and mildly taunts them on their stupidity on their inability to calculate the tip. Annoyed with Xander, a now shirtless Roy slides over the rest of the cash. Xander taunts them a little more before hearing loud crashing sounds in the bathroom. He calls out to see if Colm is okay, but before he can go investigate, the bathroom door is destroyed and Colm in the form of a hairy, muscular caveman attacks and knocks out Xander.
Xander wakes up to find the hairy creature lying on top of him and yelling in his face. Kip, Hunt, and a now shirtless Roy slowly back away, terrified of the caveman. Suddenly the creature stands up and emits a primal yell. Almost immediately, Kip, Hunt, and Roy are overcome with violent convulsions as they begin to devolve into Neanderthals themselves through both painful physical and mental transformations. Some transformations that we see include backs hunching over, hair growing longer, teeth turning crooked and yellow, brows thickening, and an extreme surge and increase in growth of body hair including on arms, legs, back of hands and feet, back, and chest (the last two areas only known due to Roy being half naked at the time of the transformation and caveman Hunt later being seen only in his underwear.)