LONDON — Presenting the agreement she had negotiated for Britain to leave the European Union, a process known as Brexit, Prime Minister Theresa May told Parliament on Thursday: “It is a draft treaty that means that we will leave the E.U. in a smooth and orderly way on the 29th of March, 2019.”

The laughter that followed from the chamber, customary for the House of Commons, was soon reflected on social media in posts that mixed ridicule and frustration with the country’s latest political crisis. Mrs. May had received grudging support for the deal from most of her cabinet, followed by high-profile resignations in protest.

By the time Mrs. May finished answering questions from lawmakers on Thursday, the mood online was clear: #brexitchaos and #brexitshambles were top trends on Twitter in the afternoon.