I've just been undertaken as I came off a roundabout near to home. Imagine me indicating right as I went round the roundabout, till I switched to indicating left as I turned off at 2 o clock. I then suddenly saw in my left eye peripheral a car overtake me on my left! How this idiot missed hitting me, or me hitting the idiot I don't know! The red mist came down and I went after the idiot, flashing my lights in an aggressive manner. Thankfully the idiot stuck his/her hand out and gave an apologetic wave. If it'd been a rude gesture things might've got out of hand. I'm seeing more of this undertaking these days, mainly on dual carriageways, but the other week some idiot actually undertook me on a narrow single carriageway!