No adults in the room allowed, is very clearly referring to all the people who claimed there were adults in the room to "manage" trump, preventing him from doing way more harm than he did.
Normally I agree sarcasm needs a /s, because of Poe's law that says:

without a clear indicator of the author's intent, any parodic or sarcastic expression of extreme views can be mistaken by some readers for a sincere expression of those views.

But in this case the reference should be clear enough, that anybody should know the context, and clearly be able to identify it as sarcasm.