Mouse.end()

#include <Mouse.h>

void setup() {
  pinMode(2, INPUT);
  //initiate the Mouse library
  Mouse.begin();
}

void loop() {
  //if the button is pressed, send a left mouse click
  //then end the Mouse emulation
  if (digitalRead(2) == HIGH) {
    Mouse.click();
    Mouse.end();
  }
}