It depends. In my work office, people tend to make enough 'disposable income' to have 'costly hobbies' so I could tell them flat out. Anyone else, or if I don't feel like it, or don't feel like justifying it, I just say "Well, you see I have both arms and legs... that means they're still waiting on my firstborn." Depending on the company, I may also throw in something like "They may be waiting awhile... "