Trust me, you may not feel much from the K, but other people most definitely know you're
fuuuucked up. Zombified. In terms of watching other people who are fucked up on drugs, people who are on K are among the most disconcerting to be around.
Don't heat solutions for injection unless you have to. That's for black tar heroin, mostly. Powder heroin, cocaine, ketamine, etc. don't need heat and in fact the heat is actually worse from an HR perspective as there may be crap in there that's only soluble in hot/warm water so you're actually getting MORE contaminants not less. It's a myth that heating your drugs sterilizes them, too, you'd need a lot more sustained heat than lighter under a spoon, and might potentially destroy your drugs in the process.
Also of course what
@MsDiz said goes without saying. All users of needle drugs have probably done questionable shit but it should be discouraged.