Growing up I had two siblings, which changed right before high school. Now, with five siblings, I couldn't ask for more. But when you have siblings there are some things that are not okay.
1. Telling them they're hot
While I understand you find them attractive, I do not want to hear how "hot" or "sexy" you think they are. One, it says nothing about their character and is a vain observation of them in general. And, just saying, all it makes me do is cringe. I do think they might be handsome or pretty, but I would never describe them that way.
2. Picking on them
No one picks on my siblings except me. Their friends might be an exception, but I will not let them be bullied or picked on maliciously. If I pick on them that is one thing because I never do it to hurt them. Someone else doing it is unacceptable.
3. Questioning if we're related
My family is a medley of half and step siblings, meaning we may or may not look similar. I've never cared about the extra words, and just call them my siblings. There is no need to cross-examine anyone on how their family is related. Whether it is adoption, marriage, or anything else: they are family. Don't make it weird when it's not.
4. Brown nosing after you did something wrong
Let me make one thing clear: cozying up to me after being a piece of crap to my family will only make me more upset. If anyone I love is hurt I turn into an over-protective mama bear. Trying to butter me up is not going to work in your favor, and neither is coming to me instead of asking them about something first. I'm not a messenger or someone to bother.
5. Comparing us
There is some frustration in being expected to do things because they did. Everyone has their own strengths and a name; I'm not just someone's little sister. Don't compare my ability to do something with theirs.
And after hearing one of these things it's a bit frustrating, almost like your soul has left for a few seconds, or just mass confusion. But, at the end of the day, you're still alive, trust me.