Maybe implement a "Star Abuse System" that would check for a number of Star/unstar events. possibly 3-5 sets on the same post, or that many star/unstar events within a time period, say for example 5 diffrent star/unstar events within 5 min.

I can see the use for undoing them by accident, or even for a temp highlight, but without wanting it on the wall.

This would prevent the rapid star/unstar behavior, but keep it for the "accidental" or other use. 

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In trying it out, I see that there is a timeout on how long you can retract a star, so it is at best fun for a few minuets.

Even then seemingly random stars get people to look back and read the conversation to see what was funny, so I am not convinced that "hiding" one star messages off the wall would be good.