Telephone calls, by far, especially job interviews or other high-stress stressful ones. Usually, i try to write a script for the phone call in case my fluency goes to crap, ill just read from the script. Instead of having to try of think and talk. I just read and talk. And its spaced out for syllables to help keep me slow. Or talking to a pretty girl for the first time. Way too many embarrassing stories of that going horribly. Sometimes i REALLY hate talking