DeSean Jackson -- GOES HAM AT CELEB HOOPS GAME ... Drops 42 Points

DeSean Jackson didn't just show up to LeSean McCoy's celeb basketball game this weekend -- HE DOMINATED ... droppin' 42 points in a triumphant return to Philly.

The former Eagles wide receiver was the talk of "Shady Weekend" -- McCoy's first annual fundraiser to benefit ALS research.

Tons of stars came out for the event ... including Nelly, Bobby Valentino and DJ Clue ... who all played in the celeb hoops game.

Valentino says he had a blast ... except for when he had to guard #10.

"DeSean went HAM," Bobby says ... "He was unguardable. His basketball game is serious."

In the end, DeSean's team emerged victorious ... but the big winner was LeSean's charity.