Discriminating between metallic (M) and semiconducting (S) single-walled carbon nanotubes (SWNTs) remains a fundamental challenge in the field of nanotechnology. We address this issue by studying the adsorption of the isotropic atoms Xe, Kr, and a highly anisotropic molecule n heptane on M- and S-SWNTs with density functional theory that includes many-body dispersion forces. We find that the distinct polarizabilities of M- and S-SWNTs exhibit significantly different physisorption properties, which are also strongly controlled by the SWNT's diameter, adsorption site, adsorbate coverage, and the adsorbate's anisotropy. These findings stem from the wavelike nature of charge-density fluctuations in SWNTs. Particularly, these results allow us to rationalize the unusual sqrt[3]×sqrt[3]R30^{0} phase of Kr atoms on small gap M-SWNTs and the double desorption peak temperatures of n heptane on M-SWNTs in experiments, and also propose the n heptane as an effective sensor for experimentally discriminating M- and S-SWNTs.