He was the fans' Hammer of the Year for three consecutive seasons before being sold to Spurs for £5m following relegation in 2011.
Parker admitted: "It was upsetting. In football, one thing I've learned is not much surprises you but I didn't expect West Ham fans to boo me.
"They obviously see it as me going to a local rival. Maybe it was the heat of the moment in a derby but I thought I might get a better reception for the time I spent there.
"I was disappointed but won't dwell on it - maybe people have short memories.
"I had four fantastic years there and West Ham will always have a special place in my heart."