Eren was fed up. Hange would go out of her way to annoy him just to witness his titan form. He realy wasn't fond of turning into 50 ft tall Titan.

"Come on Eren. Do it for science!" Hange cooed.

"Damn it Hange, i said no!" Eren snaps. You simply bear witness to all this chaos.

Hange shooting an arrow at eren was the last straw. The boy transformed right before their eyes.