Sam,
Flight attendants do some things that aren't permitted of passengers, such as moving about the cabin when the seatbelt sign is illuminated. However, given the circumstances you describe, there's really no excuse for taking the seat and not putting on the seatbelt. Refraining from holding a drink during the takeoff is a matter of both regulation and professionalism. It's also a matter of setting a good example for the passengers.
The seat belt issue is regulatory, and safety related. The flight attendant doesn't have the option of forgoing the belts and harness. It's a requirement. I don't have the option of forgoing the seatbelt and shoulder harness in the pilot seat, either.
I can't tell you what course to take; do as you feel best.