It is well known that in an M/M/1 queueing model where customers strategically decide whether or not to enter a queue, and if and when to renege, under a first-come-first-served regime, customers' selfish behavior produces an outcome that is socially suboptimal. Optimality could be achieved by adopting a different queuing regime. In particular, optimality is achieved by any regime where a new arriving customer is put in a position that is not the last. The priority slots regime, is also universally optimal. Under this regime, there is a sequence of slots indexed by the positive integers. A new arriving customer who enters the queue occupies the available slot with the smallest index. At any given time the customer occupying the slot with the smallest index is being served. A new customer who finds the first slot vacant preempts the current service. Once served, a customer leaves the system and frees the slot she occupied.