From the other side of the pond, I find this tendency for understatement impressive. If anything, it gives one more headroom for expression. If understatement is “normal”, and direct statements are a kind of exaggeration, then overstatement must be a whole other tier we don’t even have in the US: we have to say that part louder, instead.

Edit: I also read that sentence as: “I’m putting you on notice with ample room to save face, but ignoring my generosity is going to come off as very rude.”