Jalen Brunson had the best reaction to his old college teammate, Josh Hart being traded to the Knicks ... 'cause he absolutely freaked out -- yelling, "OH S***!!!"
The Portland Trail Blazers traded the former Villanova guard to the Big Apple on Wednesday ... in exchange for Cam Reddish, Ryan Arcidiacono, Sviatoslav Mykhailiuk, and a 2023 first-round pick.
Brunson was back at Villanova's campus -- where he played from 2015 to 2018 -- to have his #1 jersey retired when the deal went down .