*Though used in Canada, it is not only Western Canadian slang. It is used commonly in the US ranging widely from NY to California since the late 70's (if not before that).
Western Canadian slang meaning to discard in an uncaring fashion. Also means to discredit, disrespect or otherwise judge unworthy of consideration. Likened to throwing something unwanted in the dirt.
Suzy and I were going strong until she up and dirted me one day. I never saw it coming. I'm gonna dirt her to everyone she knows ... payback's a bitch.