Just out and out slow walkers - like your Lawrie Maddens of walking - I can deal with. No idea why you're going at that pace but that's up to you and I can overtake.
It's the people who walk about half a pace out of step. So you'll see them 100 yards down the road and you're gradually gaining on them. But when you get closer....if you carry on at the same pace then you're going to spend a while literally breathing down their neck, which looks weird. If you want to overtake then you're probably going to have to break out into a little trot to go round and then get sufficient clear air, which makes you look like a right impatient bastard.
These people need wiping out (or walk on the opposite side of the road to me, whichever is easiest)