Jean Claude Juncker has warned member states against having informal secret negotiations with the British government
Nigel Farage told fellow MEPs "you're not laughing now" as he was jeered and booed at an emergency meeting of the European Parliament to discuss Brexit.
The UKIP leader said they should be "grown up" and accept Britain’s decision to leave the EU after 43 years.
He also warned the UK would not be the last country to quit the 28-member bloc.
Offering a tongue in cheek "thank you for the warm welcome", Mr Farage said: "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?"
During a highly-charged session, Mr Farage declared: "The reason you are so upset, the reason you are so angry, has been perfectly clear from all the angry exchanges this morning: you are in denial.
"You are in denial that your currency is failing," he said.
"You are in denial over Mrs Merkel's call last year for as many people as possible to cross the Mediterranean into the European Union, which has led to massive divisions between countries and within countries.
"But the biggest problem you have got... is that you have, by stealth, by deception, without ever telling the truth to the British or the rest of the peoples of Europe, you have imposed upon them a political union."
Earlier Mr Farage was heckled as he was being interviewed before the meeting.
Speaking in the parliament, he told MEPs: "I know that virtually none of you have ever done a proper jobs in your lives, or worked in business, or worked in trade, or indeed ever created a job."
Former Belgian prime minister Guy Verhofstadt, now an MEP, retorted: "Lets be positive, finally. We gonna get rid of the biggest waste in the European Union... your salary.”
Mr Farage made his comments after the President of the European Commission, Jean Claude Juncker, rounded on UKIP members, asking them: “Why are you here?”
Mr Juncker went on to say he was banning any informal and secretive negotiations on Britain's departure from the EU.
He told the special session in Brussels: "I want the UK to clarify its position, not today, not tomorrow at 9 am, but soon. We cannot allow ourselves to remain in a prolonged period of uncertainty."
In the meantime, he said there will be no secret meetings between UK, national governments and commissioners in the corridors. "I ban that."
German Chancellor Angela Merkel has said she will use "all her strength" to prevent the EU drifting apart in the wake of the Brexit vote.
In an address to the German parliament, Ms Merkel said she expects Britain will want to maintain "close relations" with the EU once it leaves.
But she also signalled it could not expect a business-as-usual approach. "Whoever wants to leave this family cannot expect to have no more obligations but to keep privileges," she said.
Prime minister David Cameron will face EU leaders for the first time since the referendum when he joins them for talks in Brussels later.
He is expected to urge heads of state and EU institutions to be "constructive" about negotiations over a new relationship between the UK and Europe.
However, he will reject calls to immediately trigger the formal process for Britain to leave the EU - insisting it is a matter for his successor, who may not be in place before 2 September.
European Council President Donald Tusk stressed negotiations would not begin until Britain had formally triggered the withdrawal process.
"We have a ready-worked plan but I would like to underline very, very clearly that without notification from the UK, we will not start any negotiations," he said.
Earlier, British health secretary Jeremy Hunt, who may run for the Conservative leadership, has suggested Britain could hold another vote on the leaving the EU.
He said the next prime minister should be allowed to "negotiate a deal" with Brussels that the public can have a say on through a second referendum or a general election.