Is it normal to instinctively brace up any time a parent walks into the room?

TL;DR: first time being invited to a friends house, every time his parents walked in, I fully braced up and talked super formal, whilst he was super casual. And apparently he said they thought I was super nice but looked like "I had a stick up my arse".

I guess I had a mixed childhood, nothing extreme ever happened, definitely don't think I've been "neglected" or "abused". Spent a lotttt of time on my own, between the ages of 11 and 17, I was invited to a friend's house once, but that was just our friend group and his parents were out. Always been afraid to mix my friend and home lives together because of my mother. Everyone I talk to always says how abnormal it is to hide the fact I have friends from parents is.

I'm 18 and it honestly feels like my life just started, 2025 has been a complete year of firsts, I guess catch up of the last 8 years of social exclusion.

Uni is the main thing, still live at home because of personal finances, so I've tried to push extra hard to do ECAs (im only in 2 days a week because my cheapskate school cant afford professors), and met some pretty caring people that actually like me for me, for some reason. Because I wish to get closer with these newer friends, I've bit the bullet and asked mother if it's alright to bring some people over.

She was super ecstatic (because the total number of days I get home before 1am per month can be counted on two hands) and shes always telling me how unsafe it is, and how its so much better if they come here because its safe inside. And she was relieved telling me she legit thought I would be lonely for life and she didn't even know i had friends (simultaneously last week she was saying how she never trusts these "kids" i hang out with till late on the highstreet)

I've invited a total of 6 people over in the last 2 weeks (up from 0 my whole life) and now I've been returned the favour, a dinner at my mate's place.

I dressed in a casual sports jacket, jeans, shirt and goofy tie, but walked in and bro was in a onesie, and his dad asked why I was so formal.

We sat in his room then played some ps5, he was superrr casual all on the couch with his legs everywhere lying down, just chilling, i was just in some regular gaming posture, but his mum walked in asked if i wanted food, and I just reflexively straightened up my posture and crossed my hands talking to his mum (she's Bengali so i thought respect was super respected) but this guy was still just lounging on his couch.

Same thing happened a few times that evening, where it was me and him chilling, parent walks in, I sit up properly and he's still lying down.

The next day, he says "yeah they really liked you, said you were really kind and formal, but they thought you had a bit of a stick up ur arse" I was like "thanks I guess, but I just do that normally"

I had NEVER given any consideration to this in my life before tonight, which is why I'm posting this, but now that I think of it, every time ANYONE my superior walks in on me in any room, no matter what I'm doing, I always brace up and do some straight posture, un cross my legs, sit like a literal NPC. (I do the lowkey autistic / adhd whatever thing of putting your legs up in weird ways, never been diagnosed or anything)

So yeah I'm not looking for an analysis or diagnosis, just is it common, for anyone, to completely change sitting positions when you know an authority is looking at you?