If your dad is an ally, and you trust that he would support you, I would tell him first and ask for his help to tell your mother. If your mother is ',vaguely transphobic' as you've said, I'm assuming that she might not understand what being trans is. You should look up local support groups for trans teens and their families. Or at least some group counseling to help educate your family and how to adjust. Even your dad, who you've said was an ally might need some time to process everything. I hope that your family is willing to support you and accept their child for who they are. I hope the best for you.

I am a pretty laid-back guy, generally, but once on the road....
Poor drivers in general - improper lane usage, not using their turn signals, stopping at yield signs/traffic circles, failure to yield to merging traffic, driving significantly below the posted speed limit, etc.
Much of the traffic issues (in the US at least) are a direct result of people not knowing how to drive properly!