I always loved the homage to sci-fi, novels, movies, and memes in the old fallout games. There are lots of stuff i would like to see for a good laugh, at the same time i want as much of it as possible to be kept secret from me until it happens. Anyways i got a few ideas of my own.

Both random encounters, and unmarked or marked smaller locations like the café of broken dreams etc.
For example(s):
Suggestion 1:
Did you know Bethesda made terminator games back in the 90's.....? This could be fun to exploit

How bout a li'l homage here? Let's say you could stumble across a "dead" terminator-like robot in the wastes (named R-null)..... and with it lies a unique weapon... Like.. a lever action shotgun, or a minigun... ;D OOOOOOOOOOR........... one "warps" in right in front of your eyes... and requests your "Clothes, your boots, and your hunting rifle, and asks about someone named "Connor" (and if you have dogmeat, it might ask you "What's your dog's name?) Where you have get the dialogue option to say it's named "Wolfie"! Upset him and you'd have to fight him. Loot him and get energy cells, and scrap metal. (since they warp in with nothing).
Suggestion 2:
(more of a quest actually. Since Vegas was a melting pot for showmanship i would hope some of it lived on after the bombs... even if it is the least appriciated type....you guessed it... Ventriloquism! I give you: The Ventriloquest!)
The quest involves an NPC with split personallity disorder, who kept his sickness at bay by channeling his "evil" peronality through a ventriloquist doll. BUT: the doll has now gone missing, and his "evil side" has taken over his contious mind. However, his sub contious mind is desperately calling for help to free him. Trying to find someone to help him find his doll. This manifests itself through him talking and crying for help in his sleep. (nighttime) and also by ghost writing in note form, and holotapes in his house (from when he has been sleepwalking). Also other NPC's can hint on this by mentioning that he suddenly went mean and cold hearted and such. The split personality NPC will be very mean and hostile in his dialogue when talking to him during the day, so the playwer will kinda have to figure things out by visiting at night and looking through his house. (the "mean side" could hint that he used to be a doll by some funny and grim dialogue though)
Upon finding the doll, the NPC will regain "sanity" and present some kind of appropriate reward for the players trouble. There is alot of options for hillarious dialogue and ventriloquist jokes in this quest, and personally i'd find it very entertaining.

Cheerio.