The speaker is stuck near someone who hurts them, and the poem shows how that harm feels in the body. The other person is described through sharp, metallic images: hair "streaked with daggers," lungs filled with iron, breath like a "shot of poison." Even her presence seems to injure, and the title, "Toxic," makes the point plainly.
What gives the poem its tension is the speaker's trap. The urge is to run, but running "makes it worse," because she "gets off on the fighting back." So the speaker's only strategy is to go still, endure, and wait. The line about being "willing to ache and burn and die" is flat and weary rather than dramatic, which makes it feel more believable.
The mood is tense and airless, with a quiet exhaustion underneath. The ending offers no escape, only the hope of an "opportunity" to "finally hide." Relief is imagined, but it hasn't arrived yet.