Fabio Jackson is having a moment as the ultimate Michael Jackson lookalike ... and with the biopic buzz heating up, some fans are taking it way too seriously. We caught up with Fabio and his wife in L.A. Monday ... who told us about a wild run-in when a woman came up to him -- thinking he was actually the real late icon -- proclaiming "I knew you weren't dead!" It’s not a one-off -- Fabio tells us people genuinely do double takes all the time ... and his recent viral meet-up with Jaafar Jackson