How to be assertive with a naughty 5 yr old!! He takes me for a ride. Shouting or showing aggression is not really my style.

This is normal and totally healthy - your LO is seeing how far they can push the line before they get scolded/punished. Next time it happens, warn if it happens again then they will not get xx (favourite toy, tv time, favourite snack, other). Then follow thru. They will soon learn... and if they don't increase the impact of the punishment until they do. Good luck!