This is bullshit, MD

Medical advice from a med school friend

Say you're an average, run-of-the-mill human. You work out but you aren't some roided-out strongman. If you continued to apply twisting pressure to a forearm (i.e., an Indian burn—a strangely racist name for a children’s prank), would your victim's skin give way and split into two... tubes of arm skin?

No. The collagen in your skin is oriented in all directions to allow for full range of motion without tearing outright. What would probably happen is a shearing of the capillaries and small blood vessels leading to significant bruising and pain. But you could possibly have some tearing of the epidermis. The layers of the skin are too well-connected for the tube phenomenon, however.

Why do otherwise out of shape, middle-aged men have well-defined calves?

We all have very little fat in the calves to cover up the muscle (it's not a body part we need to keep warm, evolutionarily). And one of the muscles in your calves is made up of slow-twitch muscle which gets exercised every time you walk. So even if they have a beer belly, they’re probably still walking around and building that muscle with no fat to hide it.

Does the amount of a virus matter when getting ill? Like, ceteris paribus, what is more likely to make you sick: a tiny drop of liquid with a virus in it that’s dropped on your tongue or a guy with the virus projectile vomiting straight into your mouth?

It is probably dependent on the amount of the virus. Our body is pretty good at killing individual cells that happen to get infected, and the more viruses ingested, the more likely that one will slip through the cracks.

Say you are sitting on the floor. I put my feet on your shoulders and wrap my arms around your neck. Could I physically deadlift your head off of your shoulders?

Maybe? So the things you'd have to separate are: (1) the dermis & epidermis of the skin of the neck, (2) the Platysma muscle (which is very thin), (3) the Sternocleidomastoid muscle (which is thicker), (4) the Scalenes muscles, and (5) the Trapezius muscles (which are the thickest). And that's all before you even think about the vertebrae and spinal column, which are probably tougher and are also anchored by muscles up and down your back. So can you do a Mortal Kombat fatality? Probably not. But if you tear through all those muscles you might cause a bulged disc or maybe (with some twisting force) cause serious spinal cord damage that could result in quadriplegia or death.