Well, I honestly don't know if the OP was disturbing other passengers or the inflight service, but nothing described here would warrant filing an incident report. If the crew member asked you to sit down on more than one occasion and you did not comply, then i could see how it might be warranted. Otherwise, it sounds like a flight attendant on a power trip. I would also wager that this flight attendant did not share the sentiments of other crew members on the flight. It is certainly very inappopriate when a crew member decides to have a hissy fit in front of passengers.

The FAA report probably has no bearing on your Homeland security status, but it does seem very unnecessary. It may even have been a hollow threat. However, I do agree with the flight attendant that you should have purchased a second seat. You could have called reservations prior to the flight and maybe they could have unlocked two of the MVP/Gold or airport-controlled seats for pre-assignment. Just because the seat map is full doesn't mean there aren't unassigned seats. Being a mother myself, I just cannot imagine traveling with an 18m/o lap child while being pregnant. It must have been hideously uncomfortable.