Two words

It was the first day of school after summer vacation. The kids had all arrived in the high school sophomore English class, and were chatting away, making new friends. THEN…In walked a very stern looking English teacher and a hush fell over the room as the kids scurried to their seats. The stern teacher silently panned his gaze across all the kids. After about a minute or so, he spoke... "From the outset, I want you all to know that there are two words that are absolutely unacceptable in this classroom.You cannot use them as you recite, or in any of your papers, tests, or homework. Using these words even once, will get you a failing grade for that quarter. The first one is "gross"and the other one is "cool". Are there any questions?"
After a few moments of silence, this gawky teen at the back of the room raises his hand and the teacher calls upon him.
In a pubescent croaking voice, the kid asks, "So, what are they?"