“get off someone’s back” = stop criticizing someone all of the time
“Hey, get off my back. I’ll get a job faster if you stop bothering me.”

“get cold feet” = become nervous about something
“I think she’s getting cold feet about marrying my brother.”

“a social butterfly” = someone who enjoys being around people
“She’s a real social butterfly and always seems to make friends so easily.”

“in the black” = in good financial condition with no debt
“The company has been in the black for the past six months.“

The life of the party: the person who makes a party really exciting

Throw a party: have or host a party

Eat you out of house and home: be difficult to feed because someone is eating so much food

Hit it off: get along well

Just in case= It's just a precaution= Just to be on the safe side= better safe than sorry

Hold one's breath: nín thở

“hit it off” = get along well, become friends
“After the first couple of letters, I knew we would hit it off because we had so many things in common.”

“nothing to write home about” = not exciting or interesting
“My trip was nothing to write home about. I didn’t have much fun, and it was kind of boring.”