This is really difficult. Here it is:
There is a weapon somewhere.A shotgun for example. There is a barney that is standing in your way. If you go and "use" him without the gun he will not let u troug. If you have taken the shotgun and go to barney and press the use key on him he will step back.
I did it with a trigger_multiple but I don't want it happening when you go near barney I want it when you "use" barney