Why don’t kids listen to me but listen to the other teachers? That really hurts.

Before I quit, a couple students disliked me because I was too hard, stern and one would throw fits when they have to work with me. At first I was told I was too nice to those kids and now I’m HARD and very stern and too strict. One little boy rad running around with his pants and I shouted his name. Then I walked over and told him “That’s not appropriate. Pull your pants up.” He refused and I said, you need to do it NOW! But he yelled “NO! I don’t have to listen to you tubby!” I was shocked on what he said. He did pull his pants up half way. The other staff said, “(his name) pants on.” He said “okay” and just did it. Wow really? He didn’t do it when I told him too but did it for the other teachers. Another student put his backpack on and I told him, “Um are you supposed to have you back back on?” He said he said it’s almost time to go home. I told him to put it back but he just ignored me and kept going. The staff told me to be FIRM and try again. I did and he still won’t listen to me. She shrugged and had the “oh well” look and didn’t help me. The teacher came back in and sternly told him to put his backpack back and he did right away. Man why don’t kids EVER listen to me?