He would literally tell them to slow their words and ennunciate everything (which no one in real life does to that degree).
Plus, giving some actors their lines the day they arrive on set, with no context, and sometimes, not even the costar to play off of, like the famous Terrance Stamp story, "I gave Natalie the day off." Holds up a stick with her face on it. "Just talk to the stick." "What's my character like?" "Umm... You're Bill Clinton... Action!"
Stamp attributes it to the worst, most degrading experience he's ever had working on a film.