This actually happened to me last week. It's not really a sketch of sorts, but I found the whole thing mildly amusing and thought I'd write it down.
Ext. Tesco petrol station - Early evening
Ben is being driven into the petrol station in a taxi. Ben intends to get some money from the cash machine. Ben see's a lone figure walking into the car park.
Ben: (Thinks) Oh God! It's Hayley, my ex girlfriend!!!
The taxi comes to a halt near the cash machines.
Ben: I'll just be a minute, mate!
Taxi driver: Okay!
Ben leaps out of the taxi and struts over to the cash machine.
Ben: (Thinks) I wonder if Hayley is behind me? Ah well, who cares. How much money do I need? £10 should do.
Ben finishes at the cash machine and then turns to walk back to the taxi. He sneaks a glance at someone who was behind him in the queue.
Ben: (Thinks) It is Hayley! Ha Ha! It's so obvious that she still wants it. God, I look good tonight!
Ben then struts over to the taxi. After going to the drivers side by mistake he walks round to the passengers side and gets in. The taxi driver suddenly looks up in the direction of the cash machine.
Taxi driver: What's going on here?
Ben: What?
Ben looks round and then suddenly sees Hayley at the side of the car. She is holding out a £10 note.
Hayley: I think you want this!
Ben takes the £10 note off her.
Ben: Oh....uh...thanks
Hayley trots off. The taxi starts up.
Taxi driver: Well that was very honest of her, wasn't it.
Ben: Thats my ex.
Taxi driver: Oh that's your ex?
The taxi driver then points at a woman getting into her car.
Taxi driver: Cor! How about her for a new one then?! She’s got a nice wobble! Eh? Eh?!
Ben: Um, yes.