
Crook
Negative Connotation
When calling someone a 'crook', it insinuates they're untrustworthy and possibly involved in illegal activities. 
Informal Usage
'Crook' as a term for a criminal is informal and may be disrespectful in certain contexts. 
Not for Minor Offenses
Use 'crook' for serious dishonesty or crimes, not for minor rule-breaking or mischief. 