UKIP's Nigel Farage has told the EU Parliament "let's cut between us a sensible tariff-free deal", then we will be your best friends.
Mr Farage also told fellow MEPs "you're not laughing now" as he was heckled and booed at the emergency meeting of the European Parliament to discuss Brexit.
The UKIP leader accused them of being "in denial" about the euro crisis, immigration and the imposition "by stealth, by deception, without ever telling the truth" of a political union.
Offering a tongue in cheek "thank you for the warm welcome", he told them: "When I came here 17 years ago and said I wanted to lead a campaign to get Britain to leave the European Union you all laughed at me.
"Well I have to say you're not laughing now are you?"
Nigel Farage tells fellow MEPs "you're not laughing now" at emergency European Parliament session to discuss Brexithttps://t.co/OqPgw44H7W
— RTÉ News (@rtenews) June 28, 2016
As the session was disrupted by constant shouts of dissent, Parliament President Martin Schulz was forced to intervene, warning members that "one major quality of democracy is that you listen to those even if you don't share their opinion".
Mr Farage prompted particular fury when he demanded a "grown up and sensible attitude to how we negotiate a different relationship", and declared: "Most of you have never done a proper job in your lives."
He was told the comment was not acceptable by Mr Schulz, who chastised the heckling MEPs for "acting like UKIP".
"I understand you are getting emotional, but you are acting like UKIP normally acts in this chamber so please don't imitate them," he ordered.
Mr Farage retorted: "UKIP used to protest against the establishment and now the establishment protests against UKIP so something has happened here."
He said the vote to leave offered a "beacon of hope to democrats" across the continent and predicted the UK "will not be the last member state to leave".
If the EU failed to conclude a "sensible tariff-free" trade deal with the UK, "the circumstances would be far worse for you that it would be for us", he added.
The UKIP leader found himself in agreement with EU chiefs on one front, arguing that the UK government "should not spend too long" pondering how to withdraw.
Earlier, European Commission President Jean-Claude Juncker asked the UKIP politicians why they had attended today's parliament session.
"We must respect British democracy and the way it has expressed its view," Mr Juncker said in a speech to parliament, words that were greeted by rare applause from the UKIP members present.
"That's the last time you are applauding here ... and to some extent I'm really surprised you are here. You are fighting for the exit. The British people voted in favour of the exit. Why are you here?" Mr Juncker continued, breaking from his speech text.
"Why are you here?" Juncker asks UKIP politicians attending a European Parliament session https://t.co/zfmPMnfWB2https://t.co/NLcM00ylRw
— RTÉ News (@rtenews) June 28, 2016
Mr Juncker spoke from a desk next to that of Mr Farage, who followed the largely French and German speech with headphones and with a British flag planted in front of him.
Before the session began, Mr Farage had gone over to speak to Mr Juncker. Both men appeared relaxed and as Mr Farage made to leave, Mr Juncker pulled him close and gave him an air-kiss on the cheek.
Nigel Farage and Jean-Claude Juncker shared some heated exchanges today in the European Parliament. #Brexithttps://t.co/7MzLuay9bQ
— RTÉ News (@rtenews) June 28, 2016
Mr Juncker said he would make no apology for being "sad" at the result of the British vote - "I am not a robot," he said, "I am not a grey bureaucrat."
He urged Britain to explain quickly what it wanted from the EU in terms of a new relationship but insisted he had told his staff to engage in no preliminary talks with British officials until London engages the two-year mechanism for leaving the EU.
"No notification, no negotiation," he said.
On a rare personal note, the 61-year-old former Luxembourg prime minister, struck out at critics, notably in the German press but also among east European governments, who have called on him to stand down following the Brexit vote.
"I am neither tired or sick, as the German papers say," he said. "I will fight to my last breath for a united Europe."
It comes ahead of British Prime Minister David Cameron facing European leaders at a European Council summit in Brussels for the first time since the UK voted to leave the European Union.
Which trade model could Britain try to replicate after leaving the EU?