I think it often depends on what is intended, and what harm was actually done. If one is wilfully offending one’s parents, then it is probably an act of sin, though its graveness could be argued. If one is disobeying one’s parents because one’s parent is irresponsible, and unknowingly leading you down a bad road (like a drug addict parent who makes their children do drugs, or an abusive parent who abuses a child, etc.) then it is probably not sinful, as long as you remember to give them the respect they deserve as your parents, and you do so without unnecessarily offending them.
