tenterhooks, obvious, disagreeable, and black

“I’m not seventeen anymore,” Landy said, “My birthday was last week. If you paid me any kind of attention at all you would have taken note.”
“Don’t be disagreeable,” Biff said., “I bought you something, after all. I just forgot to give it to you,”
“Oh, I’m all in tenterhooks. Where is it?”
“Er…er,” he started.
“Another black moment in the history of Biff and Landy. You’re lying, aren’t you?”
“Why do you say things like that?”
“Isn’t it obvious? I told you I’m not seventeen anymore.”