Dubious

...doubtful, ambiguous, arguable, chancy, debatable, diffident, disputable, dubitable, equivocal, farfetched, fishy, fly-by-night, hesitant, iffy, improbable, indecisive, mistrustful, moot, mootable, obscure, perplexed, problematic, questionable, reluctant, shady, skeptical, suspect, suspicious, trustless, unassured, uncertain, unclear, unconvinced, undecided, undependable, unlikely, unreliable, unsure, untrustworthy, untrusty, vague, wavering...

I didn't know that there were so many synonyms of dubious until I did an online search at www.dictionary.com.

And these are the exact words I would like to use on a certain shady character who has just joined the school. Not only because of his sneaky behaviour and questionable qualification, but you know what? He dons dark-coloured long sleeves shirts over a tee all the time in this hot weather everyday! Yes, you've read my mind. I wonder what kind of tattoos are on that body. Nananana...it's not what you're thinking....definitely, absolutely not in an amorous way, okay?!!