TheVaultDweller
Front line cannon fodder
I don't think a universal rule can apply, seeing as every character has different amounts of screen time, feats, writers penning them etc. For me, it depends on how much of an outlier it is, and how many contradictory showings there are.
A good example of this is the last season of Agents of Shield's finale, where Daisy survives an impact that, quite frankly, would have left a super soldier a bloody, broken mess. And she barely sustained any injuries, other than a few cuts and scrapes. But, while she has consistently shown some degree of enhanced durability, none of her other durability feats come even close to this. Not even remotely. And she has also been hurt by less on multiple occasions.
So, personally, that's not a showing I would fall back on when discussing her durability in a forum fight. I'd rather use examples like taking hits from human form Ghost Rider and Kree soldiers, which is a lot more consistently portrayed in the show. Now, if she didn't have all those other feats that consistently portrayed a different level, then I would be more inclined to give that final feat some weight.
Or with Luke Cage, for example. If he only performed one or two headslap KO's, but had to punch people 99% of the time, I'd throw out the headslap KO. But because he does it consistently (especially in Season 2) to the point where even Claire remarked on his ability to do so, I still consider it a valid feat for forum fights, even if he doesn't do it every single time he KOs someone.