Ooh! Umm... no I've forgotten it

Mr. Bonobo had been befallen with some more unwellness, and so I was once again left alone with his class.
Thankfully, Jeffries was not in either so I was hoping for a quiet time.
But as I went over the process of how ox-bow lakes are formed, there was one boy, Symms, who just kept talking in a loud voice and making noises.
"Boring!" he was saying, and: "Ox-bow lakes are a load of cock, my dad said so."
After a good fifteen minutes of this, I'd had enough.
"Right you," I said, firmly, "outside, now!"
He rolled his eyes and sloped out of the door.
I followed him out intending to give a stern talking to and ram some discipline up him.
"Right-" I started, but I was interrupted by his mobile phone.
"Yeah?" he said when he answered it, then, "Macca you cunt! Woss hapnin'?"
I tapped him on the shoulder and asked him if this was an appropriate time to be having a phone conversation.
"Do you mind?" he said and glared at me, then into the phone, "eh?... oh just some wanker..."
The conversation continued for a further half an hour and then the bell went and he headed off to lunch.
"...And let that be a lesson to you," I shouted after him as the others filed past.