Cameron Crowe isn't America's most talented director, nor is he the most prolific, but he's a quote factory. Take his most commercially successful film Jerry Maguire (please, take it, but leave us Almost Famous). For an emotionally manipulative film about characters most of us can't relate to with an undeserved Oscar it spawned numerous memorable quotes: show me the money, help me help you, you complete me, you had me at hello — it never ends. If you've never seen the film you can basically understand what happened by connecting the dots. If we have a favorite quote, though, it's "don't shoplift the pootie." We learn, from context, the "pootie" is short for Pootie Tang, as in Renee Zellweger's ladybits. In addition to being a bad thing to do, morally, JPECH let us know why taking the pootie could be a bad aftermarket upgrade.
I'm going to have to say adopted kids, normally I'd say just kids in general, but the question specified aftermarket so adopted kids. We've all seen the ads for an awesome sports car that some poor schmuck has to sell because he's having a kid, so that he can buy some poor performing minivan or suv, THEN when you factor in the cost of maintenance on said kid you are talking about a screwing in the purest sense of the word. Even if the kid doesn't force you to sell your sports car, you're still looking at a pretty significant chunk of weight it'll add, which only gets worse as time goes on, until eventually the kid weighs as much as a full size adult. AND THEN as if all that isn't bad enough, there isn't a car dealer or buyer that will let you leave the kid in the car at trade in, you're going to have to remove the kid and return the car to stock, AND install the kid in your new car, so that kid isn't going to just ruin the performance of your current ride, but ruin the performance of every vehicle you have for the next 18 to 20 years.
Seriously, don't steal the pootie.