Possible Clues:

• Routine performer
• Joker, an impudent cad, so funny!
• One making jokes at a farmer's market?
• Comic astounded, in camp in resort
• Pa miscounted and played joker
• What's more, in revolting places, a demonic criminal is the one laughed off stage perhaps
• Rivers e.g. hold water -- guide across channels?
• Most of those in 9 across and 25 across might be laughed off the stage
• Rivers, perhaps Po and Cam used in opening to television broadcast
• He does mad pun in act possibly