One man pushback is definitely an unsafe practise. Here, it is, 1 man on airtug, one on headset and one to disconnect towbar and bypass pin and standby for visuals.I personally encountered a situation when after removing the towbar and bypass pin, I stood in direct visual contact with the cockpit while my colleague was on the headset. After disconnecting the headset, he had problem closing the headset panel(B737) and was trying to close it.The capt saw the airtug(which was parked on the capt side with back facing a/c) and decided to power up and taxi. Luckily, I( FO side) ran infront of the a/c and gave brakes on hand signal. My colleague wet his pants when he heard the engines spool up.
And if you are doing a headsetless pushback, it's always better to use the standard ICAO handsignals rather than flashing torchlights. Proactive, but very limited in usage and prone to miscomm.