good grief. 
Something is really wrong with some of you. 
If you look at the pix, you can see that Swift is separated from the DJ, and leaning into the DJ's GF. You can CLEARLY see that the guys arm is DOWNWARD.
It is NOT around her waist or back. 
Now, was it purposeful? 
Well, that trademark is in the way (and probably purposefully done), in which the M appears to be running down the side. 
If you look on the other side, you can clearly see that her skirt hangs on her, it does not poke out. As such, if that really is her skirt, then SOMETHING lifted it up.

All in all, it is pretty obvious that you have a dirty old man who thinks that it is OK to grab woman because he is used to doing that. If that was my daughter, I would be Pi55ed like her mother is. Taylor is obviously sleeping around and that is OK because she is an adult. But that does not give ANYBODY reason to grab her like that. EVER.