She likes your reaction.

You feel mildly insulted by her laughter. She sees the look on your face and tries to stop laughing to explain herself. She isn't succeeding.

Ellen manages to compose herself enough to stammer out an apology, “I’m sorry. I just didn’t expect you to get so… excited… by this.” An evil glint entered her eyes, “Although I guess I should have. After what you did in the bedroom the night of that party in high school.”

Once again your eyebrows made an attempt at orbit. “Y… you were awake?” you managed to stutter.

“Long enough to see you blow your load all over the bed,” her face held a disgusted look on it, but a hint of a smile flickered through once or twice.