The prime minister said Labour was a "laughing stock" as she poked fun the "traingate" story.
Last month, Jeremy Corbyn was filmed sitting on the floor of a train complaining about "completely ram-packed carriages".
But CCTV was later released showing him appearing to walk past empty seats.
Theresa May said everything Mr Corbyn says "tell us all we need to know about modern Labour".
She said: "The train's left the station, the seats are all empty, the leader's on the floor - even on rolling stock they're a laughing stock."
Theresa May mocked Jeremy Corbyn over the responses he got when he asked his Twitter followers to suggest questions for Prime Minister's Questions.
"I thought I would look to see what sort of responses he'd received," she said.
"Lewis writes 'Does she know that in a recent poll on who would make a better Prime Minister, don't know scored higher than Jeremy Corbyn?"
Mrs May added: "What we do know is whoever wins the Labour Party leadership, we're not going to let them near power again."
Jeremy Corbyn challenged Theresa May on house prices at Prime Minister's Questions.
The Labour leader said rising house prices had made owning their own home a "dream" for many people.
He also said the Government was failing to deliver on a "one for one " promise to replace every council house sold under the Right To Buy scheme.
Mrs May said house building was up under the Conservative government and disputed the "one for one" claim, saying the commitment had been met.
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The Labour MP accused the prime minister of "putting this House and this country to shame".Read the full story ›
The prime minister is facing the Labour leader in the first post-Panama papers PMQs.
David Cameron may also face questions over the position of the culture secretary after it was revealed he had a relationship with a sex worker.
- This live event is now finished
Labour leader Jeremy Corbyn has appeared in the House of Commons wearing a 'heart unions' badge.Read the full story ›
The prime minister responded to Labour's questions about Google's "sweetheart" tax deal by blaming the previous Labour government for failing to collect funds from the internet giant.
"We're taking about tax that should have been collected under a Labour government," David Cameron told Labour leader Jeremy Corbyn at today's Prime Minister's Questions.
Watch David Cameron's passionate defence of tax collection under the Tories:
I'm absolutely clear that no government has done more than this one to crack down on tax evasion.
...We've put in place the diverted profit tax that means this company and other companies will pay more in future and more than they ever paid under Labour, where the tax rate for Google was 0%.
Mr Cameron also said that the Conservative party has raised an extra £100 billion from businesses by changing tax laws.
Mr Corbyn accused the prime minister of failing to answer his question - whether he disputes that Google is paying around 3% tax in the UK.
Watch live as David Cameron answers questions from MPs in the House of Commons from midday.Read the full story ›
David Cameron made an embarrassing gaffe by apparently admitting to parliament that income equality had fallen under his leadership.Read the full story ›