Prat

"Harry, you prat," said Ron, "you didn't take that song thing seriously, did you?"
- Ron to Harry (GF26)

"Been having a nice little chat with her about whether or not I'm a lying, attention-seeking prat, have you?"
- Harry (OP12)

"But we didn't think Mum could take us leaving school early, not on top of Percy turning out to be the world's biggest prat."
- the twins (OP12)

a pompous prat (DH30)