  We consider a possibility that $R$-parity violating interactions of particles
which do not involve the first generation have large (up to 1) coupling
constants, $\Lambda$. Such couplings, if exist, could have a number of
phenomenological consequences: renormalization of $b-\tau$ mass ratio,
generation of $\nu_\tau$ mass in MeV region, {\em etc.}. In Grand Unified
models, where $B$- and $L$-violating couplings appear simultaneously, the
proton decay can be forbidden in virtue of hierarchical flavor structure of
$\Lambda.$ However, due to Cabibbo-Kobayashi-Maskawa mixing this decay is
induced already in one-loop. Present experimental data give the upper bound
$\Lambda \ltap 10^{-8}$ (or $|\lambda' \lambda''| \ltap 7\cdot 10^{-16},$ on
products of certain $L$- and $B$-violating coupling constants, in more general
context). The bound can be avoided, if there is an asymmetry between the $L$-
and $B$-violating couplings of usual matter fields. In the $SU(5)$ model the
asymmetry can be related to the doublet-triplet splitting.
