Leaving aside that indicators are a whole other sin, in terms of misuse, people think they have to indicate before getting to the roundabout when they are going straight-ahead. Wrong.
That's not signalling your intentions.
That's setting yourself up for a collision. If you're going left, signal left.
If you're going right, then signal right.
But if you're going straight through, wait until you're in the roundabout before signalling where you're getting off.
Most of us know the road code basics, but changes, including roundabouts and the give-way rules, have prompted people to fixate on a distortion of the rules, convinced they've got it right. Look it up.
You don't need to buy the Road Code - it's all online.
You might get a surprise - and you might find out why people end up shouting at you as you leave a roundabout.