Bent "BMX Style" Chainring

take the ring off, and place on something flat
if it is bent, put back on, take a large adjustable spanner. slip on bent bit, do up tight, bend* back in place.

*gently

Back in my good ol bmx days we didn't even used to take the chainring off the bike, put a rubber mallet on the chainring in the bent bit, hit with proper hammer until bend goes away...job done!

Both techniques are quite effective but CJ's isn't advised if you are uber precious about your BB ;p