Theresa May branded Labour a "laughing stock" as she mocked Jeremy Corbyn over his summer train woes.
Mrs May also poked fun at the Labour leader being outscored by "don't know" in a poll asking who would be the better Prime Minister.
Mr Corbyn used Prime Minister's Questions to warn of a "housing crisis in Britain" as he repeatedly pressed Mrs May on the issue.
Mr Corbyn became embroiled in a row with Virgin Trains last month, which erupted after the rail operator released CCTV images that appeared to show the Labour leader walking by vacant, unreserved seats before he complained on film about crowded carriages.
The Opposition leader had claimed the train service was "ram-packed" and hit back against Virgin Trains' suggestions.
During the first PMQs session since the summer recess, Mrs May said of modern Labour: "The train has left the station, the seats are all empty, the leader is on the floor - even on rolling stock they're a laughing stock."
Mr Corbyn opened the pair's exchanges by warning that the average house price in Britain is £215,000 - more than eight times the average wage.
He asked Mrs May: "Isn't the dream of home ownership for many people just that - a dream?"
The PM defended the Government's housing policy, insisting they want to help people own their first home, and claimed house-building is up under the Tories compared with the previous Labour administration.
Mr Corbyn countered by saying house-building is now 45,000 a year lower.
The Labour leader also said only one in every five council houses sold under Right to Buy is replaced, short of the Government's "one-for-one" pledge.
He pressed Mrs May to commit to "one-for-one" replacement.
The Prime Minister claimed Mr Corbyn was "wrong" and the commitment has been delivered.
Mrs May added: "I did notice you had asked all your Twitter followers what questions you should ask me this week so I thought I'd look to see what sort of responses he received.
"I have to say the first one was quite good - in fact you might want to make sure you stay sitting down for this.
"Lewis writes 'Does she know in a recent poll on who would make a better Prime Minister, 'Don't know' scored higher than Jeremy Corbyn?'.
"What we do know, whoever wins the Labour Party leadership, we're not going to let them anywhere near power again."
Former chancellor George Osborne joined Tory colleagues on the backbenches to watch PMQs, a far cry from his position close to David Cameron just a few weeks ago.
He saw Mr Corbyn continue to press on with his housing questions, as he warned the Citizens Advice Bureau believes one sixth of housing benefit goes to private sector landlords renting out "unsafe homes".
Mr Corbyn told Mrs May: "Do you think this really is a satisfactory state of affairs?"
The PM replied: "If you think housing benefit is actually such a bad thing, why was it when we changed the rules on housing benefit the Labour Party opposed those changes that took place?"
She said changes are taking place to allow councils to tackle bad landlords, among other measures.
Mrs May went on: "I recognise, as every Member of Parliament in this House will, the problems that people sometimes have when they're living in accommodation that is not up to the standard we would all wish to see people living in.
"That's why we're looking, changing the rules and ensuring the regulations are there."
Mr Corbyn noted: "Well, that's extremely interesting because only a year ago you voted against a Labour amendment to the Housing Bill which quite simply said all homes for rent in the private rented sector should be fit for human habitation."