simple...
f.e. create names of entity like
entity* ship;
entity* rocket;
entity* asteroid;

then attach action to asteroid
if hit me ...
and you == rocket -> bum
and you == ship -> bounce etc.

or you may create defines...
define group,skill1;
define ships,1;
define rockets,2; etc
and then attach groups to entitys
my.group = ships;
my.group = rockets; etc
then in asteroid action...
if impact...
if you.group = ships -> bounce
if you.group = rockets -> bum