I've never heard 'sketchy' used to refer to persons directly before. The acquired drug-reference understanding from the 'vague; incomplete' meaning of sketchy doesn't seem a long stretch though, now does it. Not really a coinage [looking skeptically].
The 'sketchy incident in the toilet' is a little confusing. This (seemingly) refers to the act of taking the drugs (e.g. chasing the dragon or snorting snow) rather than the affect thereof - so, it seems you've been very free with your employment of sketchy.
I guess your usage comes from the original meaning in a drug-related context, as such:

- You were messed last night! You remember singing on the tables?
- It's pretty sketchy


BTW, anyone here read the excellent article in The Economist about the drug industry?