1. Yes, locus standi can be a ground for rejection of plaint. The plaintiff must show that some right of the person has been violated. Such violation should also end in some injury caused to the person. If no right has been violated, the person won't have a locus standi for filing a suit.
According to the doctrine of locus standi, a person who is stranger to a disputed matter cannot be allowed to interfere in the judicial proceedings. Only a person whose legal right has been violated, that is the aggrieved person against whom a decision has been pronounced, is allowed to bring an action in the court.
It is necessary to note that the fundamental requirement for instituting a suit involves that person suffering from some kind of an injury. This injury can be the consequence of the act done by private parties or the state act. It is noteworthy to mention that the injury we are talking about can be either actual or anticipatory by its nature.
In the case of Shanti Kumar vs Home Insurance Co (1975), the Supreme Court of India had observed that the term “aggrieved person” does not mean a person who has suffered any imaginary injury but it means that the rights of the person have been violated adversely in reality. It means the injury must be physical, mental, monetary, etc and not mere an imagination.
Traditionally the rigid view of locus standi was followed and according to which only the person who had any direct interest in the matter could bring an action in the court. But in the 20th century, there emerged a parallel viewpoint of the locus standi that is the relaxation of locus standi.