Trecho de ssh (1) manpage:
~C Open command line. Currently this allows the addition of port
forwardings using the -L, -R and -D options (see above). It also
allows the cancellation of existing port-forwardings with
-KL[bind_address:]port for local, -KR[bind_address:]port for
remote and -KD[bind_address:]port for dynamic port-forwardings.
Portanto, ~C
seguido por -KL80
cancela o encaminhamento de porta no seu exemplo.