I love this one. I can totally comment on it.
Swallowing stuff (non sexual guys) is different for everyone I've found. They are not so much preferences, but weird aspects of a person's physiology or autonomic firing that makes them unable to swallow shit in a certain way.
Case study: 2009, somewhere on the streets of Lowell, myself and a girl-friend of mine had just bought a bunch of Hydrocodone pills to get well, as that was all we could get in town on short notice. We each needed to swallow 12 a piece, APAP be damned at that current moment. I got mine and instantly guzzled down all twelve without issue. She couldn't, under any circumstances, swallow a pill the size of a Vicodin without a ton of water. So, we had to get more money to get her a bottle of water, which took two hours.
In that same sort of vein, some people cannot handle the taste of powerful drugs of any kind. They immediately make them gag and start puking. Don't get me wrong, I would want to rinse my mouth out after eating raw meth, but I could potentially do it. However, this is a fairly moot point, as if I were to do Meth here and now, I would insufflate it by default.
So, some people really have to find creative ways of administering it if for whatever reason, oral is how they want to go.