1. Individuals who possess IQ's under the standard cut off line of 70. 2. a person who is so retarded looking that their head is shaped like that of your office's communal water cooler. 3. That 50 year old guy with thick glasses who lives down the street in his eighty year old parent's house and runs with limp wrists.
Water coolerheads must often wear adult diapers because they have yet to master the elegant art of toiletry.
In a tabletop game, a murderhobo is a player who murders NPCs indiscriminately. This is normally derogatory, referring to a player who totally ignores quests, dialog, backstory, trade, world building etc.
The term is most common with Dungeons and Dragons, but it can be applied to most RPGs where the player is allowed to kill most quest-giving NPCs and NPC traders. E.g. Elder Scrolls, Fallout, Divinity original sin.
DM: The sad little orphan girl tugs at Steve's trenchcoat to get his attention, and ask for help saving her pet dog from...
Steve: I'd like to roll a strength check against strangling the orphan.
Dave: I call dibs on the dog.
DM: You murderhobos disgust me.