I'm not going to pretend like this is a list for everyone. It really is my sincere hope that I'm one of the few people on this earth that has been put in a position where this is even an issue. But on the off-chance that this can help someone in a similar situation with their roommate, or significant other, or child, here it is: the definitive guide to telling the difference between masturbating with a steak and having sex with a dead cow.
This is just baseline stuff here. If the cow still had its skin, they were definitely having sex with a dead cow.
A small cut of the rump, leg, or ribs of a cow is a steak. A rotting bovine corpse is a dead cow. But those are the extremes. What about a cow carcass cut into threes? Are those "cuts of meat" or "still a dead cow body"? I leave it to you to draw that line where you see fit, but for my dollar, I'd say anything larger than your own thigh is probably still a dead animal.
I personally don't object to fondling a t-bone any more than I object to diddling a filet (I object to both). A steak's a steak. It's more a question of proximity. The closer the cut is to the genitalia, mouth, or anus of the cow, the more you should worry. Note: any direct use of those exact parts (and let's add in the intestines for good measure) is a sure sign of deliberate bestiality.
Seasoning lets you know that you're in the clear. You season meat. You do not season sexual partners. If you've ever gotten sea salt in your urethra, you'd know that. If you find someone going to town on a seasoned piece of beef, it probably means it was a spur of the moment, spontaneous, too-much-lust-too-little-patience situation, not a sexually-attracted-to-this-dead-animal situation. You can count that as a win. And in this situation, you'll take any win you can get, really.
Close personal contact with the animal while it was still living leaves a residual emotional connection to that animal, well beyond its slaughter and butchering. If this person was a farmer or had this cow as a pet, its possible they aren't seeing this as just a cold piece of meat to rub against, but instead as the last remnants of a lost animal friend / more-than-friend. Be vigilant around ALL farm animal owners.
Slapping yourself into the meat (or vice-versa) is more of a tenderizing activity; something you do to meats. However, stroking yourself against the surface of the meat (or vice-versa) shows a desire to feel animal meat against your skin. That's definitely sex stuff. I hesitated to include this, as everyone has their own masturbation methods which could explain this choice (non causa pro causa, and all that). But for those of you still unsure after the first five questions, maybe this could help tip the scales one way or the other.
Hope this helps. Good luck everyone. :(