Riding wind shadow - bad habit?

I got this yesterday from a lycra-d up mountain-biker through putney/wandsworth so I just did the same to him through clapham and it seemed to annoy him as much as it did me..

If I can't shake them easily (i.e. without killing myself) then that's what I do. If we happen to be going at the same speed and direction, then it's going to be me saving power and not the fool on my arse.