Be kind and considerate:
Try to figure out why the relative is acting that way and whether you are at fault. If you have an idea of the reason, may be you could apologize, talk it out or make up for it. Try to be understanding. May be they are going through a difficult phase in life and being all snappy with people.
Draw up you personal space:
This may be prove to be one of the best strategies. This way you single out the people who treat you rudely and draw up a wall around you when they approach you. You avoid giving them a chance to taunt you or give rude answers. Keep your space but do not let the relationship break. Act smart!
Act mature and cool:
Rude people have anger management issues. If you have a mature mind, look over their faults and act cool. When they see how considerate you are being and how their attitude does not seem to have any effect on you, they will tone down themselves. If it is a relative, you do not see very often ignoring them is the best option.
Be rude in return:
This may not be the best of alternatives but it sure is an effective one. If a person is taking an advantage out of your leniency and patience, demonstrate that it is very easy to be rude and hurting and very difficult to be polite. This may be your self defense mechanism. When they realize that you are not some one to be easily sabotaged and can respond back in the same tone, they might not dare to repeat it again.
Show that you are annoyed:
If a person misbehaves, make it a point to make him realize that you did not take it lightly. Withdraw favors or kindness so that they come to know what they are putting at risk with their behavior.