I think it is reasonable to argue that microaggressions as a label are meant to imply something that becomes accountable on aggregate ie not one instance which might on the face of it seem petty but how, when they are repeated, it builds into something much more significant. Which I think is fair. The problem is in this current world one instance is seen as enough and which is what makes the term feel ridiculous in that context.
If, for example, you were walking towards a set of swinging doors with someone in front of you and they didn't hold it for you but let it slap you as it shut in your face, that might be annoying if it happened once but if they do it repeatedly whilst holding it open for others who don't have, say, a PC then that would build up to an act of possible harassment or such.
You would log the microaggressions and then present your interpretation once you felt a more serious act of harm could be interpreted from the series.
This is clearly what DU intended by logging SP. However, two instances of removing herself from the f cr when DU is in there combined with her attempts to find a solution through her line manager wouldn't reasonable amount to conceivable harm and could also, arguably, not be considered microaggressions at all, which is why the Xmas incident was presented so differently by DU than SP. He didn't have much of a narrative and so massaging this seemed opportune.
The problem is, also, of course the NHS Fife management also believing one incident is all that is required and this is further compounded by all the SNP and police messaging, the Stonewall and Stonewall adjacent training etc which has borrowed from the idea that one incidence of racism is enough (of course it is as it not to be considered a micro aggression of any sort -- it is an aggression full stop) so it is the conflation and re-defining of terms that creates this nonsense.
This is why the legal process is so useful as it is willing to unpick these things.
Although reading the judgement of MacBride's first ET which he lost, they clearly also think one instance of what one person might label a microaggression (sending an email to a colleague wondering what is harmful about asking about a local SEEN network on yammer) is sufficient. He has won the right to appeal and looking at the appeal judgement it looks like the EAT might be more willing to unpick these ideas.