[Exolent[jNr]]

#include <fakemeta>

#define m_LastHitGroup 75

public tk(victim, inflictor, killer, damage, bits) {
    if (killer == victim)
    {    
        return HAM_IGNORED;
    }
    if (enabled[killer] != enabled[victim]) {
        set_pdata_int(victim, m_LastHitGroup, HIT_CHEST);
        return HAM_SUPERCEDE;
    }

    return HAM_IGNORED
}

That should work. If not, it stills looks better than what you had.