When you never go anywhere without your Nomex royal blue flight jacket (it was awkward running into Brian Duffy at Space Center Houston, and finding myself wearing the same jacket as him).
When the main writing utensils you use are a Skilcraft .9mm pencil and a Fisher CH4 pen, and you even own some Skilcraft .9mm pencils and Fisher CH4 pens which have flown on the space shuttle.
When you attach a velcro hook to the back of your timer, write MS1 on it, and attach it to your monitor (which is already covered in squares of velcro loops)
When your apartment's bedroom looks like this
, and you temporarily have a tunnel adapter airlock cover
and a mannequin of Rick Husband
in your living room (I'm going to be loaning those to an Air & Space museum in a few months to display with their Shuttle Training Aircraft).