The [Fair Debt Collection Practices Act](http://lawyerist.com/tag/FDCPA/) is basically a checklist for debt collectors, a list of things they must do and things they cannot do. With some regularity, someone actually breaks it up into a list. Consumerist just put together a list of 23 things debt collectors may not do, which includes the obvious:
- 3. Use threats of violence or harm;
- 5. Use obscene or profane language;
As well as the not-so-obvious:
- 17. Use a false company name;
- 21. Contact you by postcard.
This list is far from complete, but it is a good place to start. It is also worth pointing out that these prohibitions only apply to consumer debts; they do not apply to business debts. (Via Consumer Law & Policy Blog)