In the "Ice Cream Prank" vlog by Sir Geybin, he playfully tricks people by pretending to offer them ice cream that’s actually something unexpected, like a fake or unusual flavor. The reactions of the unsuspecting victims range from excitement to confusion as they realize they’ve been pranked. The vlog captures their genuine responses, emphasizing humor and the light-hearted nature of the prank, ultimately showcasing the fun side of social interactions.