我谢谢你 can be sincere, but in the right context it delivers a beautifully dry “thanks for nothing.” The polite words stay intact while the situation flips their meaning.
A convincing scene makes the failed help concrete. If the reason for irritation is vague, learners cannot hear the sarcasm. If the speaker names genuine help—谢谢你帮我……—the same words can return to real gratitude.
