I don't care about rules as such, but overtaking and then slowing without explanation, as described in the opening post, is unnecessarily dangerous for all involved.
Indeed, as is overtaking so closely (obviously to make a point) without any warning. If we want cars to give us space, other riders should do to.
My wife is pretty fast on the flat - for a 50+year old life long cyclist- (hates hills - she changes down to go across speedbumps in Sainsbury's), normally rides her lovely Roberts Tourer and gets so incensed if someone does that, that she chases them down, makes a point of giving a clear warning and then blasts past.
She (we) went past 4 power rangers on the road from Carronshore to Grangemouth the other week. They passed us like silent assassins (we were bumbling along), no warning at all and so close I think I got engaged to the last one. It was obvious they's made an effort to pass as they didn't really make any distance on us and, to be frank, were starting to hold us up. Then Mrs (after saying loudly "What was the point of that?") comes flying past me, and shoots past them (after a cheery "coming through"). The first guy sped up as I came past, but he was doomed really
. Such bad manners
It's the only time she gets competitive.