We use the idea of "hot" and "cold" in many idioms, to refer to weather, to people, and to relationships. Here are some of the more common idioms and phrases.
Weather and temperature
ice cold / freezing cold / stone cold = very cold: "This tea is stone cold!"
a cold snap / a cold spell = cold weather: "We're in for a cold snap this weekend."
cold-hearted = not be a warm person: "She is so cold-hearted, ignoring her boyfriend like that!"
cold-blooded killer / kill someone in cold blood = have no mercy for your victim: "He was killed in cold blood."
cold fish = a "cold" person: "The new manager is a bit of a cold fish. I don't know what to make of him."
Lack of enthusiasm or emotion
get cold feet = when you suddenly don't feel brave enough for something: "We wanted to go on holiday to Egypt, then my husband got cold feet about flying."
blow hot and cold = not be able to decide something: "I don't know about moving house. I'm blowing hot and cold about it."
in the cold light of day = when you can think clearly about something: "In the cold light of day, the ghost stories didn't seem so scary."
cold facts = plain facts: "Just give me the cold facts!"
leave someone cold = not be interested in something / someone: "I'm afraid that watching football on TV just leaves me cold."
throw cold water on something = destroy other people's enthusiasm about something: "We thought we had some really good ideas, but then she threw cold water on them."
leave someone out in the cold = not include someone: "While the others were playing cards, she was left out in the cold."
come in from the cold = be accepted into a group: "He's finally come in from the cold."
give someone the cold shoulder = ignore someone: "After the party,he was given the cold shoulder."
Cold War = the state of unfriendliness between the USA and the USSR after World War II: "We're studying the Cold War in history".
be out cold = be unconscious: "After a bottle of whisky he was out cold."
go cold turkey = to go through withdrawal symptoms from drugs: "The only way to get off drugs is by going cold turkey."
cold call = call someone you don't know to sell them something: "Cold-calling isn't always an effective sales technique."
cold comfort = a small piece of good news which doesn't make much difference to a bad situation: "Sales reductions of 50% are cold comfort if you don't have any money to go shopping!"
get / catch a cold = become ill with a cold: "I caught a cold last week."
Idioms using hot
Here are some common idioms using "hot":
to be hot = very popular / fashionable: "Iceland is a really hot weekend destination at the moment."
a hot favourite = someone / something most likely to win: "Red Rum was always the hot favourite to win the Grand National."
a hot tip = important or useful suggestion: "He gave me a hot tip for my interview."
a hot topic = an issue which is important: "Climate change is a hot topic at the moment."
hot off the press = very new story: "This gossip is hot off the press."
to get too hot = become too dangerous: "Things are getting too hot and the relief agencies are pulling out of the area."
a hot date = a date with someone you find very attractive: "She's got a hot date tonight!"
hot stuff = attractive: "Her new boyfriend is hot stuff."
in the hot seat = in a position of responsibility: "You make the decisions - you're in the hot seat now!"
in hot water = in trouble because you have done something wrong: "If you send that email now, you'll find yourself in hot water with the boss."
have a hot temper = to get angry easily: "He has a hot temper, so don't provoke him into an argument."
get hot under the collar = get angry about something which isn't very important: "You always seem to get hot under the collar about people's driving habits. Don't let it worry you!"
hot and bothered = feeling uncomfortable, either because it's too hot, or because you have too much to do in too little time: "She's all hot and bothered now that she's been invited to the theatre this evening."
be like a cat on a hot tin roof = restless or jumpy: "He's like a cat on a hot tin roof with all this talk about redundancies."
in hot pursuit = to follow closely: "The pickpocket ran off, with members of the public in hot pursuit."
hot on the trail = close to finding something: "The police are hot on the trail of the mastermind behind the bank robbery."
hot air = something which is not as important or true as it sounds: "What he says is just a lot of hot air - don't take it too seriously."
more (something) than you've had hot dinners = an expression to mean that you've had a lot of something: "I've had more jobs than you've had hot dinners!"