Repeating the same interrupt in AVR
As Jim Paris already pointed out you can explicitly clear the interrupt flag if the interrupt condition was triggered again during the ISR. However, that probably won't help you to properly de-bounce your button. If the execution time of your interrupt handler is shorter than the time you button bounces (what is probably the case), it would just re-trigger anyway.

Another issue you should consider is, that even very short spikes on your input could trigger the "button-event". Since you usually have several centimeters of cable to the button, don't underestimate noise issues (neighboring button for example). Using an interrupt triggered pin for button detection is kind of overkill anyway, but many roads lead to Rome...