Q: Can the parents of a girl who is proposed ask the boy to take an Aids test before the nikah (given the current Aids crisis and the behaviour of our Muslim girls and boys)?
A: Parents are allowed to request an Aids if the background or character of the boy indicates towards immoral behaviour. But if the boy comes from a normal, good family and has been a youth of good morality, then such a request will offend the boy and his party. In that case it will not be permissible to make such a request, for Islam does not allow any statement or action that hurts the feelings of a fellow Muslim.
Also note that in the case where making such a request is allowed, the boy is not under any obligation whatsoever to go for the test. In other words, this cannot be stipulated as a condition for the nikah, and he cannot be forced to go for an Aids test. If he does so voluntarily, it is his choice.