Your parents may be uncomfortable with displaying emotions. They may also feel some sense of responsibility if their children are unhappy.

You might try giving them the benefit of a doubt and the next time one or the other of them pulls that "You're grouchy" routine, look them in the eye and say "Does it seem that way? I'm actually feeling sad about [whatever it is] and I'd like to talk to someone about it. If you don't know why you are sad you can just say "…I'm feeling sad and your making fun of me makes it worse."

They'll either offer support, gawp at you in stunned silence or re-double their efforts to shame/jeer you out of your mood. Once you see how they react you'll know whether they are the appropriate people to go to for direct emotional support. If they can't support you emotionally, you can find others who will; either a counselor, trusted friend or other relative.