FWIW, I don't think Allan38103 was really talking about you in his post.
In any case, I actually flew AA this week. And I always board last so you'll never find me in your seat.
I did actually poach a seat on my DFW-MEM flight, I had 16A on a MD83, 16B was occupied but both 18A and 18B were empty so I grabbed 18A.
If the seat is unpurchased or unassigned, you're just moving, not poaching.
Similarly, if you have an agreement to change seats with someone, that's swapping, not poaching.
Moving and swapping are not really disagreeable. On the other hand, poaching - which means occupying someone else's assigned seat without asking - ought to be dealt with by nothing less than a strong verbal dope slap and unrelenting insistence that the poacher get the heck out of your seat.