Natamaan na kasi ako ng bato ng from a dumptruck dati. For some drivers, the sensation can be enough to startle them and cause a momentary loss of vehicle control [which is obviously more unsafe than just driving briefly over the limit].

Also had an incident of a spare tire falling off a truck. So as much as possible, I prefer to stay in front of them them rather than behind.

If I am doing 140 in the passing lane, and somebody behind flashes, I'll move aside. He has more capability to pass me than me staying on the lane and blocking him. Courtesy and acknowledgement lang of your and his position on the road. This of course assumes that it is safe to do so. As I said, safety is first priority.
Agree, if you cannot move aside immediately [you are still passing another vehicle], the least you can do is acknowledge that you have seen the intention of the vehicle behind to overtake by flashing your right hand signal lamp to show that you have the intention of vacating the passing lane at the soonest possible time.