In DFW, if you are on American, check in at Terminal A. (Naked scanners only in C and D terminals, as far as I know) If they ask you why you are checking in at that terminal, say the taxi/shuttle/friend dropped you off at the first "American Airlines" terminal.

This is completely believable, because everyone I know who doesn't travel regularly is baffled by DFW. FWIW, I always check in at A when I have a flight in D, because the lines in D are always really long (due to large families checking multiple oversize bags on international trips ). Go through security and take the train to terminal D.

The should also work for B terminal, but you are likely to draw more attention at B, since it is all American Eagle (local commuter flights) and they won't be as familiar with international fliers. If you do decide to go to B, you can say "The driver missed a turn somewhere, we ended up in B instead of D. But he said we could check in at any American terminal and take the train to D."

ETA: I didn't realize they added machines in A!! At least the list says A12 is still safe.