How do you get the bots to ignore you in left 4 dead

I don't know of any mods, but a legit way for all consoles is by going to the main menu, selecting "Extras" and selecting "Developer Commentary". This will start a single level for you to play. You can only use the commentary on this one level and all bots will ignore you, but attack your bot teammates. If all your bot teammates are killed, the zombies will then attack you as they normally would. But as long as you have at least one teammate alive they will continue ignoring you.

Although if you get between the zombies and your teammates you could possibly take damage. For example if a tank throws a chunk of the ground or punches your team it can still hurt you. In other words, the bots will ignore you, but you can still take damage.