Combine the salt, pepper and sugar on a plate. Lightly dip the rims of 4 rocks glasses into a small amount of lime juice, then into the salt mixture to crust the edges of the glasses.
Combine the tequila, lime juice, orange liqueur and agave syrup in a large pitcher with ice. Stir vigorously to combine. Pour over ice in the salt-rimmed glasses, garnish with a slice of lime and serve immediately.