Fellow survivors......please...I'm begging you...
If I or another survivor is getting tunneled......JUST DO GENS. That IS the counterplay....killer will get 1 kill, 3 out and realize that tunneling is not the best way to play. Yes it's boring but they won't stop tunneling while you keep throwing to save a teammate who is doomed regardless because then they get an easy 4k from over-altruistic survivors.
To the homies being tunneled, it sucks but do your best to loop and kill time for your team. This is a team game don't forget. Don't suicide on hook just eat up as much of their time as you can.
1 has to go for unhook obviously but 3 people standing around watching the dude be tunneled or taking unnecessary protection hits just throws their scarifice down the drain.