Disengaging Entirely From the United Nations Debacle Act of 2025 or the DEFUND Act of 2025This bill directs the President to terminate U.S. membership in the United Nations (U.N.) and all formally affiliated bodies. It also ends U.S. participation in all U.N. conventions and agreements.Funds may be appropriated to facilitate U.S. withdrawal from the U.N. No funds may be made available for contributions or payments to any U.N. body.The bill prohibits U.S. participation in any U.N. peacekeeping operation.The bill also repeals diplomatic immunity for officers and employees of the U.N. and for officers and employees of foreign government missions to the U.N.The bill repeals various acts related to the U.N., including the United Nations Participation Act of 1945, the United Nations Headquarters Agreement Act, and a joint resolution establishing U.S. membership in the World Health Organization.The United States may not rejoin the U.N. or any formally affiliated body without the advice and consent of the Senate. Any agreement to rejoin the U.N. or a formally affiliated body must include the right of the United States to withdraw from the agreement.