I got some black coffee down my windpipe. can that cause aspiration pneumonia?

Rather unlikely: Inhaling black coffee can cause choking and coughing but would be rather rare to promote a flagrant pneumonia. Even chemical pneumonitis would require a more toxic chemical such as volatile industrial solvents, or in a bad scenario, asbestos.

Unlikely: In a healthy young person with normal upper airway reflexes (ability to gag, cough, normal swallowing function), a small amount of coffee would be harmless. Aspiration pneumonia usually occurs in ill, bedridden or debilitated patients with impaired conciousness/gag reflexes.