on the spur of the moment - if you do something on the spur of the moment, you do it suddenly, without planning it.

We hadn't planned to get married - it was a spur-of-the-moment thing. (always before noun)

• when someone was a twinkle in their father's eye
• when something sneezes, someone catches a cold
• when something sneezes, something catches a cold
• When the cat's away .
• When the cat's away the mice will play.
• when the chips are down
• when the dust settles
• when the going gets rough
• when the going gets tough
• when the spirit moves
• when the spirit moves you
• when was a mere twinkle in father's eye
• when was a mere twinkle in their father's eye
• when was a twinkle in father's eye
• when was a twinkle in their father's eye
• when your ship comes in
• where is coming from
• where someone is coming from
• Where's the beef?
• Where there's a will there's a way!
• Where there's muck, there's brass.
• where there's smoke, there's fire
• whet appetite
• whether by accident or design
• whether or not