Oh wow if I had of spoken to my mother like that when I was a teen she would have killed me. I told her to F off once when I was around 14 and I can still feel the sting of the slap across the face I got.
Honestly(no offense to the teens here) I am finding that teens really have no respect for anyone anymore. A few years ago I was on the subway and I watched a group of teens push an older lady out of the way to get to a seat. I gave the lady my seat and ripped the kids a new one. Worse of it is, its a very common site to see these kids just have no respect for anyone or anything. Breaking things, pushing people, cussing out adults. Rolling of the eyes at everything and the amount of knowledge 13 year old kids have about sex now floors me.
My kids would get a serious butt kicking if they ever had an attitude and disrespect for others.
Sadly, this is very, very true.
I know that I'm horrible to my mother and sister at times, but I always apologize and we manage to get along and have a good time together.
However, I cannot even fathom being rude to a random person. I like to think of myself as polite and relatively mature when I'm around adults and out in public.
The kids on my bus are incredibly rude, they sit at the back of the bus everyday and belch loudly, not to mention they're very disrespectful to the bus driver (who is an absolute saint because I would've driven that bus back to the office months ago) and to everyone else on the bus. I wouldn't even expect a six year old to behave that way, let alone people in high school. I can't even comprehend their behaviour.
And about the "sex knowledge", I was babysitting an eight and five year old pair of siblings back in the summer when all of a sudden they brought up "dry humping" and how an older kid was telling a kindergartener all about it. I think my jaw might've hit the floor, I thought boys had cooties up until the seventh grade probably and as an elementary schooler, I thought they were an entirely different species.
I know that a lot of it has to do with their parents and upbringing, but I feel like society as a whole (primarily the media) has a greater role in it.
And related to the OP, my sister and I are only a year and a half apart but I buy her little things like that all the time and she sometimes does for me too. She always says thanks though, but even if she didn't, I'd assume she was just in a horrible mood that day... in your situation, I'd have just said nevermind and not given it to her since the screaming at you was a bit extreme.