I know what you mean, I had that on Sunday on my LSR I wasn't going significantly quicker than the guy ahead but enough to inch ahead of him, we were like two lorries overtaking on a motorway hill.
Exchanged a few pleasantries but then had that running whilst only a few yards apart thing going on for a short while. Awkward.
Personally I acknowledge all runners with a nod, smile, wave or if feeling energetic a heady combo of all three. I try not to overthink their response, if they ignore me it's there thing not mine they could just be tired or daydreaming, shy or just a complete stuck up themselves knob.
As I do a lot of running out in the sticks I find pretty much everyone acknowledges you even if there wry smile suggests they doubt your sanity but without resorting to stereotypes when living in London I might as well have been invisible.