Getting too close

I was observing this bison for about 20 minutes and taking photos before the bus arrived. It was grazing next to some restrooms at the trailhead to Uncle Tom's Overlook of the Upper Falls in the Canyon area of Yellowstone. When the bus arrived, the passengers got off and walked by the area where the bison was. The bison lifted it's head and watched intently as people went by. Several stopped to take pictures which was fine - they were still a good distance away. Then this guy walks directly towards the animal to pose for this picture. I was ready to see a goring. More people are injured and killed in Yellowstone by bison than by bears. Luckily, nothing happened to this guy. A few minutes later a couple of women positioned themselves in front of the bison - also just a few paces away and turned their back on it. I guess that didn't really matter because if the bison had charged they couldn't have outrun it. Bison can sprint at 30 mph!