NEW YORK -- A man was killed inside a Brooklyn bodega on Tuesday 20 September night after a fright broke out, apparently over one man not saying "thank you" to the other. The deadly argument was caught on video inside and outside a store on 4th Avenue in Park Slope. Witnesses said the violence started over, of all things, an unlikely dustup over good manners. The footage shows the beginning of the confrontation between a man in a white t-shirt, who wound up stabbed to death, and a man wearing a backpack, possibly for a job delivering food. The video is silent, so you cannot hear what they are saying, but Kharef Alsaidi, a worker at Park Slope Convenience, which sells candy and smokes, told Carlin the man in the white shirt held the front door open for the man with the backpack, and then criticized the man for failing to say thank you. "Just about not saying thank you for opening the door for him and, you know, they just started talking to each other about, you know, 'You can't do nothing!' Just threats between each other," Alsaidi said. Alsaidi said the man wearing the backpack told the man in white he never asked him to hold the door open, and that seemed to trigger the physical altercation, which spilled onto the sidewalk outside. At one point on the video, the man wearing the backpack seems to start to leave and a man in white appears to push his bike and slap him. Then, the man wearing the backpack pulls out a knife and uses it. Alsaidi told CBS2 what happened next, as the fatally injured man in white returned to the shop. "After that, just he started screaming, 'He stabbed me! He stabbed me!' and walked into the store and started bleeding all over the floor and the other guy took off on the bike," Alsaidi said. "I think it's ridiculous, honestlyu. They're always fighting over something that's not even that important. A lot of people be drunk over here or under the influence. It gets crazy," Park Slope resident Maya Murdaugh said. "This is a nice place, so this is shocking," another woman said. "It just goes to show you are not safe anywhere." Police told CBS2 the man who died was 37 years old and a permanent address for him was difficult to pin down. Witnesses said it's possible he was in the shelter system.