I would agree in general with Tom Doak that "it represents the crossing of an imaginary line of reasonableness, which would be different for each observer. In other words, I think the features in question would be okay with most players at some dosage level, but would fall into the category of "tricked up" if a certain level is exceeded ... but that level is a matter of taste."
That said, there are certain features that seemingly go overboard with enough players that the taste level is pretty well defined!
The phrase is usually used for designs by guys like Doak, Dye, and others trying to build harder golf courses that require some imagination and apply a penalty for certain types of shots. Specifically, the term often is followed by phrases like "windmills, clowns mouth, etc.) to compare a green to minature golf, whereby a missed shot may lead to a large score after hitting the windmill blade.
As far as I can tell, a green is called "tricked up" if either the first putt, initial approach shot or recovery chip cannot be played to stop anywhere near the pin, even if hit well. And especially if a shot that hits the green leaves the green or a putt gets de-greened. And mostly, if those features are in the middle of the green, which most players feel should be the "safe part" on nearly any hole.
So, this might be a combo of design and maintenance, but any wild green contours are the most likely thing to be called tricked up.
If there are other features getting that name, it might be fw with cross slope too steep to hold a reasonable shot. If ther are things like fw too narrow, or carries too far, those are usually just calle unfair, or forgotten as players go somewhere else.