These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: The apparent one-nighter between Magneto and Wasp had absolutely nothing to do with advancing the plot, and was never mentioned again in either the X-Men or Avengers books. This happened because Chris Claremont had told Jim Shooter that he was preparing Magneto's Heel-Face Turn, and Shooter thought Magneto would become an Avenger due to his power level and the fact that his children were in that team, so Shooter tried to give him a tighter link to another Avenger. However, Magneto joined the X-Men and this became a Big Lipped Alligator Moment.
Fridge Logic: OK, so you're an alien entity that has never known the concept of desire. So you decide to explore it by... having a bunch of heroes and villains fight each other? (To his credit, the Beyonder was almost as innocent as a baby at the time.)
It was implied that the Beyonder had spent at least some time spying on the normal universe - since the source of the hole between universes was the accident that created the Molecule Man, 20 years real-time (and at least a few years comic-time) passed between the formation of the hole and when he finally gathered up the heroes - and chose the heroes and villains because most of them seemed far more passionate than the average person. The upshot was essentially that they had different TYPES of passions (with the heroes being more selfless), and that by getting them to fight, he could learn just how far people were willing to go to satisfy their desires.
Hollywood Pudgy: Volcana isn't as fat to get all those insults from Enchantress. Of course the Enchantress is supernaturally beautiful, legendarily vain, and and doesn't have much use for mortals to begin with; it's entirely possible she was just zeroing in on something Volcana was self-conscious about and exaggerating it to make her feel bad. Of course, later artists tend to draw her much chubbier, so either she gained weight after the mini-series or she was supposed to be larger than the art depicted her.
One of the Wreckers refers to Volcana as a cow (specifically, he calls her Guernsey) so presumably she was supposed to look fat. A much later She-Hulk series that explored the origins of Rita Skeeter (aka Titania) also portrayed Volcana as being more obviously overweight before her transformation.
Strangled by the Red String: Colossus falling for Zsaji. Wolverine lampshades it through his interior monologue, theorizing it must have something to do with her alien chemistry.
Really, the real cause of this was the writer, Jim Shooter, who had been looking for an excuse to break-up Kitty and Colossus for some time. note Shooter was suitably squicked for the longest time with the depicted, even if as-of-yet chaste, relationship between two characters who were 20 (Colossus) and 14 (Kitty) at the time.
Villain Sue: The Beyonder. Completely unlimited power, to the point of being able to slap Galactus away like a fly, and he basically operates in a way that a Comic Book reader would. Knowing secrets such as: Not believing in Mephisto makes him go away, even though by all logic he couldn't possibly know that. Omnipotence isn't omniscience.