I treated my ex-girlfriend so badly today and it ruined the groupchat.
What did you do to her?
I just had no patience with her. It wouldn't have happened if I hadn't smoked marijuana.
Most people don't get along with their ex's, but it is still wrong to embarrass someone publicly in this fashion.  Nobody deserves to be treated badly in a group setting.  If your marijuana use is causing a lot of these kinds of social problems, it might be a good idea to cut back before meeting with others.
I don't care. It was just a group chat and she needed to shut up.
You still need to treat her respectfully. You ruined the group chat and made yourself look bad. You need to have more tact.