I address them, they need to learn to not be rude to others and I deserve to be treated respectfully. 

Same here. Some days I jump on and some days I let it go. It also depends on context. If he's just being moody and sulky in general I let him be but when he's being a jerk or snappy at bs or one of the cousins I will shut it down and point it out to him. 

I call DS out on it. He usually stops after.  Sometimes I don't even think they realize they are doing it.

All 3 of my SSs went through this stage at about 11 or 12.  I dealt with it in a number of ways. (Caveat - DH had w/e from Friday night to Saturday night and I always had plans for Saturday afternoon. So minimal exposure to tween nastiness)

• Direct rudeness - call them out on it.
• General unpleasantness - explained that I wasn't real family and if they wanted me to do fun things with them then they had to make the effort to be pleasant enough for me to want to spend time in their presence.  Some may thing this harsh but it worked.  We may never be super close but SSs are polite to me.
• Moodiness - ignore the SS completely like they didn't exist.  As in the old school sending them to Coventry. Until the attitude improved I didn't see them, hear them.

It's normal, but all because something is normal doesn't mean it shouldn't be addressed. It's normal for toddlers to not know their colors, so we teach toddlers what their colors are. It's also normal for toddlers to become overwhelmed and "throw a tantrum", so we teach toddlers how to calm down and control the reactions to their emotions.

Same goes with preteens. YSS became aggressive and mean as a preteen when his hormones first kicked in. DH took a couple of different approaches to get YSS to recognize he was getting upset and control his reaction to those feelings. It was okay for YSS to cry. It was okay for YSS to scream into a pillow. It was okay for YSS to sit in silence and clench his fists as he counted backwards from 10.

What wasn't okay was hitting OSS. What wasn't okay was backtalking me and giving me attitude. What wasn't okay was screaming at all of us, throwing tantrums, being overly dramatic, etc. He may be having "big feelings" that he doesn't have the tools yet to control, but his job (with DH's help) was to learn to control them AND EXPRESS THEM in healthy ways.

So, yes, it's very appropriate to call out poor behavior. It's also important for the parents (not you necessarily in this instance) to teach how to modify their behavior in spite of their emotions. Puberty isn't an excuse to be an a-hole. It may be the reason why a kid is a bigger a-hole than normal, especially in those preteen years when the hormones first hit (I swear for my SSs that 11-13 were THE worst). Being the reason why, though, doesn't mean it goes by unaddressed.

A little bit of both. With 2 bios and 2 SS's all teens, I catch a lot of attitude.

If I know they are having just a bad day, I will let them get away with a little more. I have bad days and I am an adult. I know I can be snippy and short with people. I let them be people. I might throw out a warning and just say "tone". 

However, if it is blatantly disrespectful I call them out quick. I try to say say something like "I realize you are having a moment right now, but you will not speak to me that way". - If they try and still be rude, I shut down the conversation and send them to their room. I won't tolerate it. 

Back in the day when I was in counseling about my crazy blended family of 5 kids and hyper DH, my counselor told me that if the teens can't act out a little at home, they will act up outside the home.  He was talking about verbal exchanges.