PHB pg 57 said:When a target entry specifies that it affects you and one or more of your allies, then you can take advantage of the power's effect along with your teammates. Otherwise, "ally" or "allies" does not include you, and both terms assume willing targets. "Enemy" or "enemies" means a creature or creatures that aren't your allies (whether those creatures are hostile toward you or not).
The first and second lines indicate that unless specified, a character does not fall into the category of his own "allies." The third line basically defines "enemies" as non-allies. Does this mean that a character can be his own enemy?