Never Use This Candy On A Gingerbread House
Despite its reputation for being notoriously difficult, building and decorating a gingerbread house is a delightful holiday tradition for most. Even if you tend to use pre-constructed gingerbread houses to save yourself the headache of baking and building it yourself, there are still obstacles to overcome. Though decorating the house might be the most fun and easiest part of the process, there are pitfalls to avoid.
One thing to consider when you are decorating your gingerbread house is where it will be sitting within your home. If the candy-laden cookie house is sitting in a room that will likely get very warm, such as near a fireplace or near the oven, then you want to avoid candies that could melt easily. While thick or large chocolate pieces such as Hershey's Kisses probably wouldn't melt so easily, thin chocolate is much more likely to ooze (via Just So Tasty). That means you'll want to avoid anything that has a very thin chocolate layer such as chocolate-covered cherry cordials (via Better Homes & Gardens).
Don't use heavy candy on gingerbread houses
The primary thing to consider when choosing which candies to use and which to avoid while decorating your gingerbread house is the weight of the candy. Though some heavy candies might not bring down the house if it is a very thick, solid structure, many houses could collapse under the weight if their foundations aren't strong enough (via NPR).
Heavy candies to avoid definitely include large chocolate-covered nuts. These might work well for yard decorations around the house, but too many of them stacked on the roof or sides of the house could cause it to be too heavy and structurally unsound.
However, the worst candy you could probably use on a gingerbread house are assorted boxes of chocolates. Not only are many of the chocolates inside dense, which could add up quickly with regard to the weight of the chocolates, but the fillings could be an issue, too. From creams that could leak out to heavy chocolate chews filled with caramel, these chocolates likely wouldn't fare well on a gingerbread house. Not to mention, the boxes are far too expensive and not very festive for gingerbread house decorations.
Whatever candy you do opt for, don't forget to use a very sturdy "glue" when attaching your decorations. NPR suggests using melted gummy bears for a tacky paste that won't slide anywhere.