Then you need to lift off the accellerator, don’t brake check or anything, just slowly slow down.
If the car behind you won’t give you enough safety margin to maintain a high speed, then your only option to maintain safety is to reduce your speed so that the safety margin they give you is enough to stop in time for an accident.
Here in Sweden we have plenty of roundabouts, I will use those to also get rid of annoying drivers who just can’t manage their distance, if I have someone like that behind me when I get to a roundabout, I just drive a full lap of the roundabout and let them pass.
I will allways let these guys past when I can, they are in a rush to their own accident, and I am not, let them pass and and make them stop being my problem, if I can’t find a place to let them pass I will reduce my speed to compensate for their lack of safety margins
Sometimes I increment my cruise control down a mph at a time to see how much I can get them to slow down
I already subconsciously do this because I know it pisses them off, but I like your justification much better