Bored teens can easily get themselves into mischief. Be sure to have activity or game ideas ready when your teen invites his friends over, in case they claim to be "bored." Your teen and his friends might be reluctant at the idea of playing games you've organized, so be sure you choose games that appeal to their interests.
Divide the teens into teams to answer a series of questions. You can ask questions related to pop culture, such as celebrities, music, television shows and movies, as well as academic questions based on what the teens should already know from school. The first team to accumulate a certain amount of points wins. You could also put everyone into boy-girl pairs to play a modified version of charades, where you ask a guy question to a girl and a girl question to a guy. For instance, you might ask the name of a celebrity clothing line to a guy. He must then look to his partner who will try to act out the answer, using only gestures.
Keep the teens laughing by challenging them to a series of silly and hilarious competitions. Divide the teens into teams of three that have to race to mummify one of their members, using white crepe streamers. The team to do the best mummy job the fastest, wins. You can also bring the teens back to their toddler days and have the kids race to see who can drink juice out of a sippy cup the fastest. Or, have a pajama relay. Each team must have everyone put on and take off an over-sized pair of pajamas over their clothes. The first team to get the pajamas through their whole team wins.
Plan a blender game that is sure to gross the teens out. Have the teens sit at a table, but keep the blender hidden, perhaps behind a little cardboard partition. Let the teens see all of the ingredients you have, then hide those as well. Blend two items, which can be anything from pears and turkey slices to spinach and chocolate syrup. Pass out the blended concoction to the teens. The first to correctly identify the two ingredients earns points. For a messy game guaranteed to garner laughs, give each teen a spoonful of peanut butter and a small plate of toasted "o" cereal. The teens must spread the peanut butter on their faces and then collect all of their cereal pieces first to win.
Social games can help the teens get to know each other better. To play two truths and a lie, have all of the kids write down two things about themselves that are true and one that is not. They should make sure that the two facts are things that they have not shared with the group, to make it harder to figure out the lie. Each teen will read all three of his statements, and the rest of the group has two chances to guess which is the lie. You could also have the teens write a statement about themselves, without signing their name. Collect the statements and read them aloud. The teens must "buzz" in to guess who made the statement.