I do not know of any pranks, but do recall rabid NPC fans chanting, e.g., when an opponent was at the charity stripe, "Your Grandma's hot!"
Not just
any opponent. The North Park student-section chant when an opponent was at the free-throw line was typically "Your Mom is hot!" It was used in particular if there were a number of middle-aged people sitting behind the opponent's bench in the crackerbox (i.e., there were obviously opposing players' mothers present). I can actually recall two or three instances when an opposing player's mother stood up and applauded, as though pleased by the public affirmation of her cougarhood.
I've also been told by a former player for a CCIW opponent that he had to bite his lip to keep his focus on his free throw and avoid laughing, because he knew that his mom was in the stands and he could picture her getting freaked out by it. "Best chant ever!" he said. "I was dying to look over at my mom to see her reaction, but I didn't dare!"
There was only one opponent that ever drew the "Your Grandma's hot!" chant from the North Park students, and it happened annually when that particular team visited the crackerbox and was awarded free throws. It was a certain central Illinois school that wears green. I'll leave it to everyone to deduce why.

A true classic involved annoying Calvin during warmups, which was led by a future NPU HOFer, with, "It is predetermined (preordained?) that you will lose."
Predestined, actually, not predetermined, in keeping with the doctrine of predestination most famously associated with (although not 100% exclusive to) the Reformed branch of Protestantism that was formed by Calvin University's namesake in the sixteenth century.
I wouldn't be surprised if Calvin fans hear predestination jokes from a lot of schools besides North Park whose students generally have a certain baseline level of biblical and theological literacy. I'm guessing, for example, that there have been Wheaton students who've yelled similar jeers at the Maroon and Gold.
Calvin's archrival Hope likewise has a pedigree from the Dutch-American subspecies of Reformed Christianity. I don't ever remember anybody making predestination jokes about Hope teams losing, though, and I'd be curious if any of the Hope fans who regularly read this board have ever heard any such jokes directed at a Flying Dutchman squad.
Good times, we lucky we got'em.

Yep. A good motto for North Park athletics would be, "Keepin' your head above water. Making a wave when you can!"
This year the Park is making waves!