[LarzI]

pawn Code:

public OnPlayerText(playerid, text[])
{
    for( new i = 0; i < MAX_PLAYERS; i++ )
    {
        if( !IsPlayerInAnyVehicle( playerid ) && i != playerid && !IsPlayerInAnyVehicle( i ))
            return true;
        else if( !IsPlayerInAnyVehicle( playerid ) && i != playerid && IsPlayerInAnyVehicle( i ))
            return false;
    }
    return true;
}

Try that