Since it's been built up over decades at this point, the MCU has built up a following that can be incredibly passionate.
From fans of the source material to those who jumped on with the original Iron Man back in 2008, it's always been a challenge for the filmmakers and Marvel Studios to try and outdo themselves with each new film they put out.
Ever since the beginnings of the MCU, the directors have been known to sprinkle in little tidbits for the audience to latch onto, whether it be just a passing joke or a certain aside that doesn't pay off until years and years later.
Regardless of how it's actually presented, these are the moments that the fanboys really thrive on, leaving everyone shellshocked once they actually see it happening on screen in front of them.
As much as these could be cheap shots just to get a good laugh, a lot of the time they go on to play a key part in a given film's narrative. They don't manage to please the fans all of the time, but the following moments of fan service can definitely lay claim to being universally loved.
10. JARVIS - Iron Man
When looking back on the history of Iron Man, people tend to forget about how integral JARVIS was to helping Tony Stark reach his fullest potential.
After all, since our favorite artificial intelligence was folded into Vision later, how the hell were you supposed to keep up with him when you had to worry about all the other side characters coming in every new MCU movie? People were paying attention to the explosions so much that most probably didn't even realize his name was an anagram.
Yeah, for as much as the name Jarvis sounds like an upscale butler in the vein of Alfred Pennyworth, the letters act as an acronym for Just A Rather Very Intelligent System, modelled after the actual butler Tony has as a kid in the comics. Though we do get a glimpse of the real Jarvis towards the midpoint of Endgame, this is the kind of Easter Egg for the comics nerd who really know their stuff.
As opposed to your casual movie fan, the acronym would probably fly over most people's heads, thinking that it's just some hoity name to give your butler and nothing else.
While most of JARVIS' operating systems have been made into Vision nowadays, this remains one of the few Easter Eggs that doesn't deserve to go over the heads of the fairweather fans.