Even if you don't follow tennis at all, you probably know that Serena Williams and Maria Sharapova have a longstanding feud.
(Some have called this feud a "rivalry," but as far as actual talent goes they're nothing close to rivals — Sharapova has not beat Williams since 2004.)
Both athletes have said shady things about one another over the years, but Sharapova in particular loves to take shots at the GOAT. In 2017, she released a memoir that focused intensely on Williams, at one point claiming that Serena hates her for being "skinny":
I think Serena hated me for being the skinny kid who beat her, against all odds, at Wimbledon.
She also wrote about being scared of Serena, noting that her body is "intimidating":
First of all, her physical presence is much stronger and bigger than you realize watching TV, She has thick arms and thick legs and is so intimidating and strong. And tall, really tall.
This is a particularly odd passage because Serena Williams is actually five inches shorter than Sharapova.