Thanks for nothing!
Urban Dictionary
A sarcastic expression of frustration or displeasure at someone/thing.
More literal definition: I have no thanks for you because you aren't
doing what I want or did something I didn't want.
Cambridge Dictionaries Online
used to show you are annoyed when someone has done something you are
unhappy about or has failed to help you in some way:

Beware of Trojans bearing gifts!
A turn on the expression Beware of Greeks bearing gifts:
Meaning: Don't trust your enemies.
Origin
An allusion to the story of the wooden
horse of Troy, used by the Greeks to trick their way into the city. It
is recorded in Virgil's Aeneid, Book 2, 19 BC:
"Do not trust the horse, Trojans. Whatever it is, I fear the Greeks
even when they bring gifts."
Of course that English version is a translation. Another translation,
by John Dryden, has "Trust not their presents, nor admit the horse."
The same thought was also recorded by Sophocles (496 - 406 BC), in
Ajax:
Nought from the Greeks towards me hath sped well. So now I find that
ancient proverb true, Foes' gifts are no gifts: profit bring they
none.
The Classics are no longer widely taught or read, so this phrase is
now little used, although it was resurrected in a sideways reference
during a 1990s copyright dispute. There was considerable discussion
then, in Internet chat rooms etc., regarding the company Compuserve,
which owned the copyright to the GIF image format, and their possible
intentions to restrict its use. Some people feared that they might be
taken to law by Compuserve if they received and viewed GIF images
without permission. The phrase "beware of geeks bearing gifs" was
coined to sum that up.
When your friends come to help but end up harming you, the "Trojan horse" is homemade, so beware of Trojans bearing gifts means:
You can't trust your friends when they come to help.
“Most of the evil in this world is done by people with good intentions.” ― T.S. Eliot
– Edwin Ashworth Feb 07 '15 at 21:49