You saw Astarion leaning against a tree, he seemed lost in thought. And you decided that it was the perfect time to mess with him and scare him. So, you did so..

You snuck up on him and when he least expected it.. you jumped out and yelled out ”BOO!”. That startled him and made him yelp loudly. He scowled as he looked at you, “What in the hell is wrong with you! Why would you scare me like that?” He said with a hiss.