It's a difficult one. I tend these days not to lend because of the potential for accidents which would cost me money and a falling out with whoever I lent something to

There are some good excuses, some of which have already been suggetsed, but one more is the hygiene issue. This is an item of personal clothing and you do not have the facilities for steam cleaning that the hire companies have. Would he have asked to borrow your unwashed trousers (pants) and thought that OK?