Sam~ You usually stand there smiling trying no to laugh until he is done, you don't find it weird really more of him being adorable. You would walk in and he will stop and be embarrassed but you tell him how it was cute.

Dean~ When you see him do something weird you record it.When he is done you stop it and walk in like you didn't see anything.Then a couple seconds later you pull your phone out and show him and he would pout like a 5 year.The both of you get a good laugh about it and you end up deleting it.....Well sometimes

Cas~ When you catch Cas doing something weird you just join him and go along with it.