Manpot said: ....... anything they perceive as aggression can cause them to attack with that tail..
I was stung in the foot about a year and a half ago. It was incredibly painful and the toxins/venom takes a long time to dissipate. I still don't have normal feeling in the area of the sting.
I would not recommend intentionally approaching a ray. In my case, I stepped on it without knowing it was underfoot.