peg (one) as (something)
To believe or consider that one definitely is a certain type of person or thing. I pegged her as a total bore when she first started working here, but since getting to know her, she's actually pretty interesting. I'm disappointed, Jake—I never pegged you as a quitter.
peg someone as something
and have someone pegged as somethingto think of someone in a certain way. Susan pegged the new employee as a lazy worker. I had you pegged as an angry rebel before I got to know you.
peg someone
tv. to gossip about someone. Kim is always pegging Jill. What’s her problem?