Nothing in general. Just repeated personal bad experiences with them in handling situations which needed a little additional care. Also their mileage accrual policies leave much to be desired.
I noticed one person saying they can't stand B.A. to fly with, I have tended to fly with them because they do not serve nuts as snacks... my son has a nut allergy.
I am just interested as to what is felt to make them a poor airline to fly with?
Consequently, I had flown them only in emergencies to get to Kolkata quickly. Now that they don't fly there anymore, that also has become a non-issue. Emirates and Etihad do the job much better for those circumstances.