"1: In case of the removal of the President from office or his death or resignation, the Vice President shall become President.
2: Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take the office upon confirmation by a majority vote of both houses of Congress.
3: Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President.
4: Whenever the Vice President and a majority of either the principal officers of the executive departments, or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of his office as Acting President.
Thereafter, When the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and a majority of either the principal officers of the executive department, or of such other body as Congress may by law provide, transmit within four day to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office. Thereupon Congress shall decide the issue, assembling within forty eight hours for that purpose if not in session. If the Congress, within twenty one days after the receipt of the latter written declaration, or, if Congress is not in session, within twenty one days after Congress is required to assemble, determines by two-thirds vote of both Houses that the President is unable to discharge his powers and duties of his office, the Vice President shall continue to discharge the same as the Acting President; otherwise, the President shall resume the powers and duties of his office."
The twenty fifth amendment gives recourse and ability to judge whether a President remains fit to continue his job as the President of the United States. The President is able to declare that they are unfit and Congress also has the ability to declare the President unfit. It also dictates what should happen if the President were to vacate his office and how a new Vice President would be chosen.
This image is a reference to the belief that the current president is unfit for his job and should resign, as he could easily be perceived as being unable to discharge his duties and responsibilities fully.
This comic is a funny little illustration of how the twenty-fifth amendment can be interpreted: if the President deems themself unable to do their job, they have to wait for an agreement from Congress.