a bad apple

meaning: a person who is naturally bad and will ruin others near him

1. He has always been a bad apple: stealing at school; trying to get his friends to take drugs; he even had a fight with his own mother.

2. Jonny is a bad apple, so stay away from him.
bad blood

meaning: deep hatred between people that started after an incident/incidents and has continued since

1. In the play ‘Romeo and Juliet’, the bad blood between the lovers’ families helps bring about the title characters’ deaths.

2. There’s quite a bit of bad blood between those two. It goes way back, so long they’ve probably forgotten what started it in the first place.

3. “Dave and Paul seem to fight a lot.”
“Yes, there has been some bad blood there since Dave stole Paul’s girl.”
(put something) on the back burner

meaning: to postpone or delay doing something because there is a more important task to be done first.

1. He has been planning to write a book for quite some time, but for now it is on the back burner because he’s busy with his new wife and child.

2. “Have you finished making your boat yet?”
“I’m afraid I had to put that on the back burner for the moment: I have a hundred things to do at work.”
back to/at square one

meaning: to have to start again

1. The boss told us our idea was stupid and he wouldn’t give us any money. I guess it’s back to square one.

2. He has been trying to get a date with her for months. It looked like she was going to give him a chance, but then he got drunk and made a fool of himself, so he’s back at square one.
back to the drawing board

meaning: have to go back to the planning stage

1. I took our project outline to the manager, but he said it would cost too much. I guess it’s back to the drawing board.

2. He really thought his new design would work, but on the very first day the prototype broke. He’ll have to go back to the drawing board.
back the wrong horse

meaning: to support one party in a competition, only to see them lose (and possibly face negative consequences from the winner)

1. He thought Dave was going to win the election, so put money into the campaign. Unfortunately it looks like he has backed the wrong horse in this case: Dave is losing by a mile.

2. When she was young she wanted to marry a successful man. She had a choice of two: Dave and Paul. She chose Dave, but it was Paul who made a million, while Dave sits at home watching TV and eating chips. She definitely backed the wrong horse.

3. Before we put our money into one of these companies I want you to do some research: I don’t want us to back the wrong horse and end up feeling stupid.
(I have) a bone to pick with (you)

meaning: to want to talk to someone about something they have done that has upset/annoyed you (usually spoken)

1. “Anne called him yesterday saying she had a bone to pick with him; apparently she heard he had been out at the pub when he had told her he was seeing his sister.”

2. “Hey, Dave, I have a bone to pick with you. What did you think you were doing telling my girlfriend I met my ex?”