All Greek to Me

A friend in college once told me that our chemistry homework was all Greek to him. Confused, I double-checked my textbook, then checked his textbook, and both were all in English.  Figuring he must have mis-spoken, I hired a Greek translator to translate our textbook into Greek for my friend.  Naturally, I sent him the bill.  For some reason he got mad at me.  Some people just don't know how to say "Thank you."