/**
 * First of get the euler angles we start from!
 **/
ANGLE* StartAngle = nullvector;
ang_for_bone(StartAngle, player, "BoneName");

/**
 * Alright now get the euler angles of the destination.
 **/
VECTOR* DestVec = vector(you.x, you.y, you.z);
ANGLE* DestAngle = nullvector;
vec_to_ang(DestAngle, DestVec);

/**
 * Calculate the difference of the start and destination position.
 **/
ANGLE* DiffAngle = nullvector;
ang_diff(DiffAngle, StartAngle, DestAngle);

/**
 * Now we have everything we need! Rotate the bone.
 **/
ANGLE* StillToRotate = nullvector;
while(1) {
    ent_bonerotate(player, "BoneName", vector(
                     DiffAngle.pan * time_step,
                     DiffAngle.tilt * time_step,
                     DiffAngle.roll * time_step)
    );

    /**
     * We gotta check if we are close to our destination.
     **/

    /**
     * For that we first get the angle we still have to journey
     **/
    ang_for_bone(StartAngle, player, "BoneName");
    ang_diff(StillToRotate, StartAngle, DestAngle);

    /**
     * Now we see if we are near the destination.
     **/
    if( StillToRotate.pan < 1.0 && StillToRotate.pan > -1.0 &&
        StillToRotate.tilt < 1.0 && StillToRotate.tilt > -1.0 &&
        StillToRotate.roll < 1.0 && StillToRotate.roll > -1.0) {
        /**
         * We are pretty close to our destination! Though to make sure
         * we really reach the destination just snap the bone to it.
         **/
        <Your Bone snap code>
        // Don't forget to exit the while-loop!
        break;
    }
    wait(1);
}

/**
 * (Hopefully) be happy
 **/