Jo Swinson launched a scathing personal attack on Boris Johnson as she accused him of being "not fit" to be prime minister.
The Liberal Democrat leader used a campaign speech in central London to launch a blistering attack on Mr Johnson, claiming all "Boris Johnson only cares about Boris Johnson".
Ms Swinson said the prime minister had repeatedly shown he does not care about anyone apart from himself, using the example of jailed British-Iranian mother Nazanin Zaghari-Ratcliffe as an example.
"He will do whatever it takes, sacrifice whatever or whoever is needed to get what he wants," Ms Swinson said.
"His life has been about becoming prime minister. Not out of some burning desire to make people's lives better, but out of some sense of Etonian entitlement, because it's what people like him get to do.
"Boris Johnson doesn't care about you and your family.
"Just take the case of Nazanin Zaghari-Ratcliffe - a British mother wrongfully imprisoned, a small child devastated, separated from her mum.
"When he was talking about that case, his words would be used against Nazanin at her trial."
She accused Mr Johnson of having "Etonian entitlement" who was even willing to "lie to the Queen" to suspend parliament in order to get his own way.
She also highlighted the endorsement of the prime minister by English Defence League founder Tommy Robinson.
"Boris Johnson is not fit to be Prime Minister. not just because he doesn't care, not just because he lies, but also because he is complicit in stoking division and fear in our communities.
"Why else would Britain's biggest racist, Tommy Robinson, be supporting him?
"Honestly - such an endorsement would shame any decent person but Boris Johnson has no shame when it comes to the language he uses about race."
She also compared Mr Johnson to the US president, saing that we have our own "British Trump".
"Whether it is the sexist, patronising crap of comparing elite women athletes to wet otters, or him bragging about patting his female boss on the bottom ... this man isn't someone our sons can look up to, that our daughters can have faith in.
"Boris Johnson is not fit to be Prime Minister."
When it was put to her that Mr Johnson refuses to say how many children he has, Ms Swinson said: "I have two children, by the way."
Ms Swinson tried to put a positive gloss on a poll showing that the Lib Dems may only gain one seat at the election.
She said: "What this poll shows is that there are 134 seats where either the Liberal Democrats are in first or second place as things stand.
"That shows there's a huge amount to play for."
Ms Swinson was asked by ITV News Correspondent Rebecca Barry if she could learn anything from the prime minister, after a recent poll put Mr Johnson on course for a parliamentary majority.
She said: "Boris Johnson is someone who is prepared to say what ever it takes.
"He's not fussed about what he says is what he believes and what he'll do.
"That's not a strategy I want to emulate. I think its important that I stand true to what I believe in, that our party stands true to what we believe in."