We deduce a comparison theorem for certain quasilinear operators from Bony's strong maximum principle. Such operators include mean curvature operators in various geometries. As applications, we prove, among others, a nonexistence theorem for minimal hypersurfaces in a wedge-shaped domain of the Heisenberg group and a rigidity theorem for minimal hypersurfaces in pseudohermitian cylinders. This is joint work with Hung-Lin Chiu, Jenn-Fang Hwang, and Paul Yang.