Question:

Is there any evidence the MIBs (Men In Black) actually exist?

Answer:

There is an equal amount of evidence that aliens impersonate or are the real MIBs (Men In Black) and that the US military personnel sometimes masquerade as MIBs to scare the abductees into silence. The arrival of MIBs depends on the gravity of the situation and which group, alien or military, feels most threatened by what the civilians witnessed.