Re: How can they top the Hulk/Loki "fight" in Avengers 2?
Not quite a 'fight', but my attempt at a similar comedy beat...
So, during an earlier battle (possibly pre-acquisition of the IG) Thanos is taking on the team in a fierce battle, but abruptly stops paying attention to them, and starts having a deep, involved discussion with Death... which of course, occurs on another plane of existence or in a construct of his mind, depending on how the audience wishes to interpret said conversation.
The Avengers continue their assault, but some kind of energy shield makes Thanos impervious to attack. The Avengers then temporarily cease their attack and basically just stand around looking awkward and confused. From their perspective, Thanos is just looking off to the distance and talking to himself.
Stark breaks the silence by deadpanning, "Well, they don't call him the Sane Titan..."
* Of course, for this to work, the audience must be aware that Thanos is referred to as the Mad Titan, which can easily be set up previously.