I call my sister 'sis' because it's gender affirming for her.

Chicken Wing is the preferred nickname both ways between myself and my younger brother. No clue how it started exactly.

When I was five or so, my older sister invented the word "cosweb", convinced gullible-little-me it was the worst thing ever, and called me that for (what felt like at the time) months. She eventually just stopped. I didn't figure it out until I was in grade six or something.

I call my older brother shinny piece of shit and my sister I just say something that the same level of mean as: wasup toothless (she has teeth so it's not really an insult but it's meant to be)

Oddly, I've started calling my sister's sis and brother's bro rather recently. 'It saves time on texts' is my reasoning.

I think it might be laziness mixed with too much fan translated manga / manhwa with a dash of IDGAF.

If there is a preamble of any kind, it's "Dude" followed by a story of some kind. But usually it's just like... Stream of consciousness. Like. A text will be "so, this thing happened." Or we send memes. That's it. Sometimes we say "hey".

Depending on the specific sibling dynamic, the following is also acceptable:

"Hey dickweed!"

"Fuck off. Alright what do you want?"