What it means
To push the boat out means to splash out a bit and make an occasion feel worth it. You use it when people stop doing the cheap-and-cheerful version and decide to go a little nicer than usual. Better food, extra drinks, maybe a cab home, the sort of plan where nobody's pretending this is just a normal Tuesday.
Usage examples
"It’s your promotion, so we’re pushing the boat out. No sad Tesco Meal Deal tonight, we’re getting a proper curry and a couple of pints."
"For the wedding anniversary we pushed the boat out and booked the suite with the sea view, mum cried at the breakfast buffet because dad finally said he was happy with the choice of holiday."
"On her sixtieth birthday the team pushed the boat out, hired the private room at the Italian on the high street, three courses, two bottles of red and a cake with sparklers."
"Go on, push the boat out a bit, it’s not every day your sister turns thirty and actually books a venue that isn’t above a pub."
"We pushed the boat out for Friday lunch and ended up with oysters, cocktails, and that dangerous little phrase, shall we get another bottle then?"
Where it comes from
It’s a well-established British idiom in use by the early 20th century, meaning to make a special effort or spend more freely than usual. The phrase is older in literal form, but the exact route into this figurative sense isn’t pinned down for certain, so the usage is clear even if the backstory stays a bit misty.