lane.
Whenever I see another driver signal wanting to enter my lane and there is only like 2 cars lengths or less between the car in front of me, I speed up and don't let the other driver in. Several of times I've had them honk at me for not letting them in D:
I don't know how use of indicators is taught in the US, but as I understand it, you use the indicator to indicate (to other drivers) your intention to change direction.
For example, if I'm on a busy motorway and I have to change lanes in order to get in the correct lane (for example, turning off the motorway or there's a motorway split), even though I can see the lane I'm indicating towards might be too busy to immediately get into it, I still put on my indicator so someone can see what I want to do and act accordingly (hopefully to accommodate if they're not a self-centred arsehole). That someone might not necessarily be driving the car closest to where I want to go.
I don't even think some people will look after they signal because they think that gives them the right to change lanes without regard
So your way to resolve this is to judge someone for something that you don't know whether they've done it or not. And, as someone else already pointed out, your behaviour discourages people from using indicators.