Anthere:
In american english (and in Maverick voice), I think "silly" is rather friendly. A bit like "gros béta". It is not very offending, rather a gentle reproach. Perhaps slightly friendly moquery.
Yep - "silly" isn't meant to be offensive at all.
... But perhaps would it be wise to be cautious while using this word ?
Agreed - the word does not translate well.
--mav