hot potato

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A problem that is so controversial or sensitive that those handling it risk unpleasant consequences.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable A child's game in which players pass a ball or other item between them, with the object of avoiding being left holding the item when time expires.
• noun countable, idiomatic An awkward or delicate problem with which nobody wants to be associated.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a difficult situation