If I loaned my cousin Roger some money in exchange for oral sex,?
I am not a lawyer but the contract you stipulated meets almost all the requirements of a contract to be upheld by law. A contract is a mutual agreement by two or more parties to do or not do something for an agreed upon period of time, for consideration. In this case, the terms of the contract are that you loan money to someone with the agreement that it will be paid back sometime (you actually dont stipulate this in your question). The consideration (which is usually in the form of interest) in this case is oral sex. If your cousin provides the oral sex and you dont loan the money you could be considered in breach of the contract. If he doesnt repay the money in the specified time period then he can be said to be in breach of the contract. Contracts do not have to be in writing to be enforceable but there must be some means of proving that such a contract did in fact take place. Oral contracts are as enforceable as written contracts if the contract can be proved to have been made. Note that the stipulation mutually agreed upon is critical. It cannot be coercion and there is grounds for doubt if you extort oral sex from a desperate person in exchange for a loan. That fails the test of a mutual agreement because it was made under coercion. The other party did not necessarily willingly agree to the conditions but was forced to do it. When Whitey Bulger coerced the owner of a liquor store to sell it to him at a fraction of its value or suffer harm to his family, that contract would be seen as void even though the victim signed all the legal documents handing over the title. This is a gray area and is why contract law is so often assiduously argued.