If you can't look at your "boomerang" child without seeing giant red dollar signs swirling around his head, or if she comes home from her part-time barista job just long enough to change clothes and head to a friend's beach house for the weekend, chances are you're beginning to resent your child's freeloading ways. To help restore harmony in the home and ensure that your child will eventually be motivated to find career success, be sure to treat your adult child as a productive member of the family, not a pampered guest.
Once it becomes clear that your son or daughter will be returning home after graduation, and preferably before he or she shows up on your doorstep with a new puppy and a live-in significant other, set rules and conditions for their return home, and then stick to them. Consider setting a timeframe or probationary period, e.g., "You can live at home for six months." If, despite his or her best efforts, your adult child is not financially able to leave home at the end of the time period, terms can be renegotiated, much like a lease or temp contract in the "real world."
Don't forget that you're still the parent. You aren't doing your children any favors if you continue to coddle them or try to be their "best friend." On the other hand, keep in mind that your child, as frustrating and irresponsible as he or she may seem to you some days, is now an adult.