Possible Clues:

• Class likely to face reprimand? Nonsense
• Rubbish given applause -- a trick
• Suitable charge applied after emptying canal's rubbish
• Hot air blow by mouth
• The applause, getting a bit uppish, was insincere
• A bit taken aback by the enthusiastic reception? Nonsense!
• Strike over some rising hot air
• Contrived but foolish talk
• Class liable to talk nonsense
• Mug, perhaps first to applaud rubbish