know (your) stuff

informal

to know a lot about a subject, or to be very good at doing something.

When it comes to restoring grand pianos, Mr Morley really knows his stuff.

• if push comes to shove
• if someone knows what's good for
• if someone knows what's good for them
• If someone thinks something, they've got another thing coming!
• If someone thinks something, they've got another think coming!
• If someone thinks, they've got another thing coming!
• If someone thinks, they've got another think coming!
• If the cap fits .
• If the cap fits wear it.
• if the going gets rough
• if the going gets tough
• if the worst comes to the worst
• If thinks something, they've got another thing coming!
• If thinks something, they've got another think coming!
• If thinks, they've got another thing coming!
• If thinks, they've got another think coming!
• if worst comes to worst
• If you believe that, you'll believe anything!
• if you can help it
• If you can't beat 'em!
• If you can't beat 'em, join 'em!
• If you can't stand the heat, get out of the kitchen.
• if you catch my drift
• if you get my drift
• If you pay peanuts, you get monkeys.