Seeing as how I have admin in the PWNT server, I never long-term ban for stupidity. If a noob screws something up out of pure stupidity, I slay him/her. I then explain briefly why what they did was wrong.
"sniper towers are less important that front walls and flag d, they waste pieces"
"cuboids have low surface area, dont use them flat pieces cover more space"
"this server doesn't require entrances and exits"
"if you grief my wall one more god damn time i will smack you back to china town! >

"
If they continue, I kick them. If they rejoin and continue once more, I ban them for the duration of the map (usually a 30min ban).