She was the biggest film star of the 1940's (when Lucy was merely a B-movie actress) but Crawford's career was long gone by 1967 when she was asked to do a guest appearance on The Lucy Show.
The 'plot' of the episode revolved around Lucy and Vivian inadvertently coming across Crawford's new country home, a house she's fixing up herself. They think the legendary actress is broke (in real life she practically was) and arrange a benefit show for her, which they all star in (of course).
During rehearsals for the show, Lucille Ball caught Crawford drinking from a flask in her purse. The next day, the legendary film actress was late to the set.
A shouting match ensued over the phone when Crawford was late again the next day, with Lucy threatening to fire the aging actress and replace her if she couldn't get it together.
From then on, Lucy was merciless in her criticism of Crawford's performance. The show went off all right, but it sounded like Crawford was drunk for the taping.
By all accounts, Joan Crawford needed the money and the exposure the show offered (the episode was originally written for another aged-out diva, Gloria Swanson). For that reason, she endured the humiliation of Lucy having her repeat and repeat a dance number and then, in front of an audience, rudely cut the number because of Crawford's poor performance. (The insult stung - Joan Crawford first gained attention as a young dancer in the Twenties.)
After the taping was over, Crawford was quoted as saying, "My God, they tell me I'm a bitch - Lucy can outbitch me any day of the week!"