Ik ben Sinterklaas niet (= I am not Sinterklaas)
Sinterklaas or Sint Nicolaas is the most popular feast day in The Netherlands. The Saint with his - nowadays - colorful helpers the Pieten comes with a boat from Spain and delivers presents to kids who are well-behaved.
After Sinterklaas' arrival in November, children place their shoe in front of the fire place before bedtime (called "schoen zetten"), hoping to find presents in the morning, while everyone is busy preparing poems and fabricate gifts to give to each other on 5 December.
Sinterklaas is synonym for candy, gifts and family time. Saying one is not Sinterklaas ("Ik ben Sinterklaas niet") means that someone does not hand out gifts without getting something back for it.
By the way, did you know that the American Santa Claus is based on the Dutch Sint? The Dutch settlers introduced the generous holy man in America and in the 18th century the American version with sleigh and 9 flying reindeers merged with Christmas, becoming part of the popular culture.