How to fix leaking bathroom sink drain where PVC meets ABS connection?
Try @JACK solution of cutting off bad threads. You might also try a different style slip-joint washer (they come in plastic or rubber). Tighten the fitting, hand tight is not enough. If that doesn't work, the fitting is toast. I would cut it off and glue a new one on, then use the proper slip-joint assembly with no glue, goop, caulk, goo, or any other such nonsense that is unlikely to work.

You have a couple problems though.


If you cut it off (even if you cut carefully, which you should) there will be very little pipe remaining outside of the wall. That's OK though, glue the new (1 1/2" male adapter) to whatever is left and it will be fine. Use abs glue if you get an ABS fitting, use universal or multi purpose glue if your new fitting happens to be PVC.
The PVC trap arm may end up being too short after you shorten the wall pipe (it depends how much was left inserted into the wall pipe). If so, you'll need a new P-Trap.