Here is a thread for things that are a must not do, right in front of your commissar. I will start this off with a few general ones.
1) Asking permission to retreat
2) Thinking about asking permission to retreat
3) Snort Warpdust
4) Doing any sort of drugs
5) Thinking anything heretical

6) Do not question the commissar.

7) Do not ask about dating your commissar

8) Asking your commissar "what is the big deal with the Emperor?"

9) Look like you are retreating

10. Ask for a day off (Seriously, we've lost countless guardsmen due to that.)
11. Do not think about killing the commissar. Do not even think about not killing the commissar.

12) Can i go on an toilet break.

13) Telling that stupid joke about how many commissars it takes to screw in a lightbulb

14) Asking your commissar permission to wear his hat

15) Never ask the Commisar if he's absolutely sure he doesn't need a medic. Even if Especially if he's missing an arm.