Even though Valve "removed" the ability to force characters to say different phrases (according to this post), I continue to find players in games that are still able to do this!
I know it can get annoying if spammed, but used in moderation I think it's quite funny and can add to the multiplayer experience.
How can you make your character say things (outside of the limited phrases in the selection wheel) in Left 4 Dead 2 (post the 2015 patch which supposedly removed this ability).