True story about that.
I had to ride the jumpseat home on the 31st.  I had just gotten my hair cut (ATL is a place where a 'brotha' can get his hair cut about anywhere), threw my uniform in the commuter room and put on a thin sweater.  The captain actually asked to see my license and medical (which is cool) and then the lead flight attendant kept asking me questions about if Phoenix was a 'recycle' city.
"I'm not sure, but I know that we have a co-mingled recylcable bin at the house"
Still with no real idea what or why she was asking me about recycling in Phoenix.
Then she comes back to the cockpit during boarding and asked if I was coming back from "jet recurrent".
"Nope! Just getting off a trip commuting home"
"Are you going to sit in front? or in back?"
"I've got to ride up here because it's going to be full and it's oversold".
"You can't ride in the cockpit".
"I'm a Delta guy, I can."
"When did 'in flight' get access to the cockpit jumpseat?"
"I don't think they do!" Now I'm starting to realize 'something'.
"Are you a supervisor?"
"Nope."
"How can you ride up here?"
Now the captain and the FO are starting to clue in and the poor FO is about to spit his coffee out in laughter.
"Because the captain said I could!"
"What, are you a pilot or something?"
"Yup!"
"No you're not...are you?  What do you fly?"
The FO starts laughing.
"The Mad Dog (slang for MD-88)"
"You're too young."
"I'm 34! but thanks!"
"Where are you based?"
"Here!"
"I havent' seen you in the lounge"
"Because I'm a pilot! 
"
Ahh yes, I love traveling incognito!  Perhaps I should make an ID that says "Iain Cogneeto" or something!