  Dust grains moving at hypersonic velocities of $v_{d}\gtrsim 100\rm
km~s^{-1}$ through an ambient gas are known to be destroyed by nonthermal
sputtering. Yet, previous studies of nonthermal sputtering disregarded the fact
that dust grains can be spun-up to suprathermal rotation by stochastic
mechanical torques from gas-grain collisions. In this paper, we show that such
grain suprathermal rotation can disrupt a small grain into small fragments
because induced centrifugal stress exceeds the maximum tensile strength of
grain material, $S_{\rm max}$. We term this mechanism {\it MEchanical Torque
Disruption} (METD). We find that METD is more efficient than nonthermal
sputtering in destroying smallest grains ($a<10$ nm) of nonideal structures
moving with velocities of $v_{d}<500 \rm km~s^{-1}$. The ratio of rotational
disruption to sputtering time is $\tau_{\rm disr}/\tau_{\rm sp}\sim 0.7(S_{\rm
max}/10^{9}\rm erg~cm^{-3})(\bar{A}_{\rm sp}/12)(Y_{\rm sp}/0.1)(a/0.01\mu
m)^{3}(300\rm km~s^{-1}/v_{d})^{2}$ where $a$ is the radius of spherical
grains, and $Y_{\rm sp}$ is sputtering yield. We also consider the high-energy
regime and find that the rate of METD is reduced and becomes less efficient
than sputtering for $v_{d}>500\rm km~s^{-1}$ because impinging particles only
transfer part of their momentum to the grain. We finally discuss implications
of the METD mechanism for the destruction of hypersonic grains accelerated by
radiation pressure as well as grains in fast shocks. Our results suggest that
the destruction of small grains by METD in fast shocks of supernova remnants
may be more efficient than previously predicted by nonthermal sputtering,
depending on grain internal structures.
