In Sainsbury's on Saturday, I spotted the one till that didn't have a queue and wheeled my trolley over. There was a woman standing in front of me, and a few bits & pieces left on the conveyor belt, which I naturally assumed were hers. I was just about to start unloading my trolley onto the belt when a man appeared with an overloaded trolley, pushed in front of me and said 'Excuse me, I'm with her', indicating the woman in front of me. Now, I read a lot on here about people standing in car parking spaces to reserve them, but I have never, ever heard of people reserving spaces in the checkout queue. When I look back now, I remember us both approaching the checkout from different directions and the man indicating to the woman to run ahead to get there before me. I gave him the glare from hell and went to the next till. Afterwards I felt like such a doormat. I know I should have said 'I was here with my trolley first, I am not moving' but I didn't. I know I need to be more assertive. Please tell me how you would have reacted/what you would have said?