I know this is a very old joke
But I swear this happened.
I used to work on a production line where they made cooker hoods. My chargehand, a very pretty lady who we shall call Jenny, was doing a crossword.

'Mr O'Reilly' Says Jen, 'Whats this one - To egg on, 5 letters?'. That was the clue, not like in the joke, 'egg on'.
I looked at her expecting her to say 'Is it toast?', which she did, so I laughed politely, little suspecting that she was serious and she'd never heard the joke. She shouted at me when I laughed, claiming 'well, it FITS!!!'

My Dad, bless him, shouted up to me when I was in my room one day asking what was the name of 'that pub near the college?'
'The Talbot' I answered.
'That's it, thanks' sez Dad.
'What do you want to know that for?'
'It's a crossword clue - drinking place, 6 letters, starts with ta'...
( His Popiness the Hole Invaded Poland on, Mon 7 Mar 2011, 0:09, 6 replies)

My friend's dad looked up from his crossword as I entered the room
"Stuck on this one," he said. "'A postman's round'..."
I ummed and ahhed for ages, then a thought struck me. "How many letters?" I enquired.
"About a sackful!" he yelled, and burst out laughing.

My, how I felt foolish.
( emvee cruor deo cruoris, Mon 7 Mar 2011, 10:18, closed)

To egg on ... toast?
What?

Either I'm being thick here, or that's explained very badly.

Yes I get the "Egg on toast" bit. No I haven't heard the joke.
( Je suis un vagabond is an unfunny, up your own arse middle class knob, Mon 7 Mar 2011, 13:28, closed)

oh sweet christ i'm agreeing with a vagabond.

( janet aylia y'all motherfuckers need jesus, Mon 7 Mar 2011, 16:47, closed)

if it is not toast
what is the answer then?
(whiskas loved by 8 out of 10 cats, Mon 7 Mar 2011, 13:33, closed)

Could be a lot of things, really.
Drive? Nudge? Taunt?

The clue itself is not Ximenean enough to be a cryptic one for the double meaning; something like "Tribute given at breakfast with egg on face (5)" could produce "toast".
( .Yeti. El amor en los tiempos del cólera, Mon 7 Mar 2011, 14:23, closed)

OK There may be some racial stereotyping here...
Paddy is doing a crossword. He sez to Mick 'There's a clue here, 5 letters, 'egg on''
Mick says, 'I know what it is, it's 'toast'.

Old and piss poor, I know, but I thought I'd try to repeat it here for the hard of thinking.
( His Popiness the Hole Invaded Poland on, Tue 8 Mar 2011, 22:04, closed)