Asked the gate agent (GA) at the boarding gate to print my boarding pass (BP). I was arriving from another flight on a separate ticket, so I was already airside, and needed my boarding pass for the next flight. Anyway, presented my Global Entry (GE) ID card, and upon seeing it, the GA informed me GE card is not an acceptable form of ID. She followed up asking me why I didn't have a passport or a driver's license. For the record, I don't bring my DL if I am not driving on the trip, and I don't bring my passport if I am not traveling internationally. Also, if I could find a kiosk, I would have been able to print the BP w/o presenting any form of ID. I finally got my BP in the end, but it was a struggle that didn't need to be in the first place.