Parker joined Tottenham last season in a £6million deal after four seasons with the east London club.
During that period he was named 'Hammer of the year' three times, and was also named footballer of the year by the Football Writers' Association in his final season even though the Hammers were relegated from the top flight.
The 32-year-old put in some lionhearted performances for the Hammers during his time at the club, but he was booed throughout his first appearance at Upton Park since departing for West Ham's local rivals Spurs.
The England midfielder, who gave away a penalty in Tottenham's 3-2 win, admits he was taken aback by the jeers from the home crowd.
"I didn't expect the West Ham fans to boo me and obviously it was a little bit upsetting," said Parker, who played 113 times for West Ham.
"I don't know why (they did it). I don't know if it's because I went to their local rivals... I'm not sure, but I just would have liked to think that maybe I would have got a better reception after what I did in my time here.
"I loved (Upton Park), the fans, and I loved the club.
"I had four fantastic years here and it will always be a club with a massive place in my heart. I was looking forward to coming back and I couldn't wait to go out there and play so I was disappointed (to be booed)."
Spurs moved up to third in the Premier League following the win, which came courtesy of a last-minute wonder-strike from Gareth Bale.
Parker thinks the come-from-behind victory will have served as a warning to Arsenal, against whom they play in the north London derby on Sunday.
When asked what he thought Arsenal's players would make of seeing Bale's killer goal fly in, Parker said: "It's deflating isn't it?
"I've been in that position where you're watching the scores come up (on television) and it goes 'last minute goal at wherever' and you're praying it's the other team - and it isn't, it's the team that you don't want to score.
"So it is deflating as a player on the opposite end, and I'm sure the Arsenal players are like that.
"I'm sure they'll be thinking they need to concentrate on themselves and try to win the game against us, and if they win the game against us it goes down to a point so it's going to be tight."
Parker gave West Ham the best years of his career and I think it's silly to expect him to stay at a relegated team where he was the one bright light at the time. It would also have harmed his England career. Fortunately not all West Ham fans think the same way as I saw plenty of them stand and applaud him when he came off on Monday night.- bozwell99