Disneyland in July 1997. I was 31 years old and it blew me away. I had always loved Disney before, but from that day on, I was transformed, a love affair had begun.
Went to Disneyland in the late 1960's, two trips to MK in the late seventies/early eighties, three trips to Epcot in the late 80's and ealry 90's, and then two extended trips to all the WDW parks in 1999 and 2001.