A mate of mine once did a favour for a friend. When the job was finished the friend asked, ‘How much do I owe you?’
‘Don’t worry about it; buy me a beer next time you’re in the pub,’ my mate replied.
A couple of weeks later the friend walked into the local, saw my mate and ordered an extra beer. He walked over to him and said, ‘Here’s that beer I owe you,’ and handed it to him.
It promptly fell through my mate’s outstretched hand and smashed on the pub floor.
‘Why did you drop that beer?’ the bloke asked.
‘Because,’ my mate replied patiently, ‘this is a Schooner Grip not a Middy Grip.’
Needless to say he was bought schooners from then on and they fitted perfectly.