...looking out the window while a technique is being shown...
You people get windows!
Respectfulness is paramount over formalities. I prefer being respectful but comfortable when training with others. Bowing at the begining of class and after. After sensei shows a technique and then to your partner and again after practicing that technique is all very easy and comfortable. Even using Onegaishimasu and Domo arigato gozaimashita... even saying it the equivalent in English is fine. This all conveys perhaps the minimum levels in some aspects but I find it does enough to show that you respect your dojo, your sensei, your training partners and hopefully yourself. Being able to laugh when it happens is good for a positive atmosphere and knowing when to be quiet so everyone can focus on what sensei is saying and demonstrating is common sense as well...
As mentioned some places have their 'group policy' for why you have to bow a certain way before or after sensei/sempai, back a certain stiffness, angle, right hand before left going down elbows to the mat, the left hand before right coming back up... eyes a certain level, feet move a certain way when approaching, disengaging, hand at your sides thumbs covered/tucked in... yes the lists can go on and on... especially if you factor in when you are supposed to breath in or out during all of this. This sort of thing can be fun if you want to see if you can learn it and repeat it but I find that for me personally, being able to perform that level of formality all of the time would be an atmosphere killer no matter how many times I smiled to my partners... as that can be not allowed either.
So it can get to a point where it gets to be almost counter productive to just training.