Someone came to a dead stop on a major A road merge point / slip road in front of me today for no reason. Worst part is there was quite a length of slip road parallel to the main carriageway they could have crept along and tried to merge further on but they stopped quite early on the slip road. Even when a kind van driver slowed right down and flashed their lights to let the numpty out they still didn't go! Unbelievable.