This bug confirmed in the GECK involves Motor Runner and the quests I Put A Spell On You and Aba Daba Honeymoon. Once you start I Put A Spell On You, Colonel Hsu asks you to go kill Motor Runner. The task to kill Motor Runner (it's not an actual a quest objective, optional or otherwise) is bugged and you can negotiate multiple motor-runner's helmet from motor runner for 200 caps each. The helmets are quest items and can't be dropped. You can go back and report your success to Hsu, but he doesn't remove the helmet(s) from your inventory, nor does motor-runner change his dialogue options. This means you'll be unable to complete Aba Daba Honeymoon as motor-runner is forever stuck in his bugged 'the NCR sent me to kill you' state and will never have the dialogue option to deliver him the drugs, even if you are wearing the provided Great Khan outfit. The only solution I've found is to enter "setstage 140c3b 60" into the console, which instantly completes Aba Daba Honeymoon for you. Console owners are screwed as usual. It's highly recommended that you complete Aba Daba Honeymoon before talking to Colonel Hsu.