"Deal damage to Laser Designated enemy vehicles using lock-on weapons"

I joined a Mirak 24/7 server and there happened to a guy just painting targets and I got it done quick. Try looking up servers filtered for conquest, maps with jets and helis and fast vehicle respawns. Then join a few and see if you can find one with someone painting. Im guessing he was trying to complete some other mission. If you do find one spawn as support first, throw down your supply bag and redeploy as engineer so you can replenish your stingers