You can simply check by writing the name into ur bio if you're able to it's off if not it's on the list, no way to take them off I suppose, I wouldn't know!
You can also check on Xbox one when you type a gamertag in and check if it's available. If it's not vulgar, it will say sorry the gamertag is not available and if it is vulgar, it won't say that it's taken and it will prompt you to pick a tag like you haven't entered one yet.