"No!" You shouted. "I won't let you do this to me. I accidentally came here and didn't cause you any trouble. Just let me leave."
"Hmm... Refusing to make a choice now, are you? Very well. I will choose for you."
Before you could react, the dragon's tail forcefully wraps around you and lifts you up in the air. "Enjoy your new life." The dragon chuckled. Then his tail suddenly pulled you around and shoved you with insane force up his anus. You were immediately overwhelmed with an intense tingling sensation and then... nothing.
Eventually, you came to, disoriented and trying to recall what had happened. Everything felt wrong. Your entire being felt confined to your "face", with the majority of your feeling around what seemed to be your lips, which were forced into an "O" shape. But they weren't your lips. They felt too different. The next thing you noticed was the terrible taste and smell that completely surrounded you. And finally, as your vision returned, you could see a giant scaled tail above you and the rear legs of a dragon in your peripheral. Immediately, everything came back, the reality of your situation hitting you like a brick wall. You struggled with all of your might, but couldn't make your body budge at all. You wanted to shout for help, but because of your lack of control (and a body unfit for speaking), you couldn't make a sound. You had been completely transformed into a dragon's tailhole.
"Well, what do you think?" You heard the dragon ask from somewhere above you. He laughed. "You shouldn't have rejected my offer if you wanted to avoid this." The dragon's head curled around and came into your view, analyzing your new body. "Even so, you should be grateful. Even in as lowly a position as you are now, being a part of my draconic body is far superior to being human, wouldn't you agree?"
You very much did not agree, but there was nothing you could do to protest. Instead, you were forced to feel every twitch and every movement across your new body.
As the dragon finished inspecting you, a sly grin crept across his face. "I suppose you would like to see your new position, wouldn't you?" The dragon stood up, carrying you along behind him. You couldn't see where he was going, but you could tell he was walking along his hoard of treasure. Eventually, he turned around and raised his tail. In front of you, you saw a large, highly reflective gem. In the reflection, staring back at you, you could see the backside of a dragon, his tail was raised. Right in the center was his tailhole. You. Seeing this humiliated you to no end. This was your life now. Forever trapped as a dragon's puckered tailhole against your will.