My band kids have lost the plot

Crowd-sourcing advice here...

I'm a new band teacher, and I'm kicking myself for being too nice at the start. I've got kiddos who have very little respect for themselves or each other, and only use band as a time to hang out with their friends. I'm not an authoritarian, nor have I ever been. Do I have to be one now to get these students to show some respect for anything?

These are the ones who got dead last in a parade competition and their response to the adjudicator's notes was to talk over them and (again) "hang out with their friends". I fear this only has a 'wait until the new school year/blank slate start' kind of solution. I really don't like them very much and class/rehearsals leave me angry and emotionally wrung out.

Help? Anyone have some suggestions?