Pour One Out
Explanation
The Joke
A person is at what appears to be a graveside or memorial, pouring out a drink and saying, "I'm pouring this one out for you, Sally." The ghost of Sally appears behind them, looking annoyed, and says, "Bourbon? You're pouring out bourbon for me?" The person, startled that Sally's ghost has appeared, responds, "You know what, I didn't know you were here."
The Humor
The comedy works through the subversion of the "pour one out" ritual. Pouring out a drink for a deceased friend or loved one is meant as a gesture of respect and remembrance -- the living person sacrifices a drink as a symbolic tribute. The joke is that the ghost actually shows up and has opinions about the offering. Sally is apparently offended by the choice of bourbon, implying it's either not her preferred drink or not a good enough liquor to waste on her behalf. The living person's flustered response -- essentially admitting they wouldn't have chosen bourbon if they'd known Sally was actually watching -- hilariously undercuts the sincerity of the tribute. It suggests the gesture was more performative than heartfelt, since the person would have put more thought into the drink selection if they'd known the recipient could actually judge them for it.
References
"Pouring one out" is a widespread cultural ritual of pouring a drink (usually alcohol) on the ground in memory of deceased friends or loved ones. The practice has ancient roots in libation rituals found across many cultures, from ancient Greek spondai to West African traditions, and has become a common gesture in modern popular culture, particularly in hip-hop and urban communities.