Offensive flags are the worst, aren't they?
No one is expecting you to be able to judge anything and everything, if you are uncertain of how to handle the flag, you should ping the rest of Travel.SE's team diamond and discuss it with them in your site's private mod room, there's a reason there's three of you.
If you can't reach consensus between the three of you, or just want more feedback, you should bring the issue up in Teacher's Lounge, fellow moderators and Stack Exchange employees are (almost) always there to help. And if by any chance it's something you don't want to share with 200+ moderators, you can email Stack Exchange directly and ask for guidance.
Lastly, if there's a comment/flag war going on at the time you see the flag, lock the post for an hour/day immediately to give everyone some time to calm down, but edit out the offensive remark prior to locking. Your edit can be rolled back in the off chance you later decide it wasn't really offensive.
Or, you know, do what I usually do, pretend you never saw the flag and let someone else handle it. ;P