Credit: Rick Dole/Getty Images; Mark Dadswell/Getty Images

Tiger Woods is a 33 year-old billionaire and widely considered the greatest golfer in history, but there's something that he hates about himself: his calves!

Jaimee Grubbs -- who says she had 20 sexual encounters with Woods over a 31-month period -- revealed her ex-boyfriend's body hangups to Us Weekly.

In April 2007, Grubbs had just met Woods in Las Vegas, and was hanging out alone in the entertainment room of his MGM Grand mansion.

The golfer arrived and "told me he had done a workout and he was going to do another workout for legs," Grubbs tells Us.

Observing the athlete, Grubbs sassed back, "I said, 'For someone who works out a lot, you sure have small calves!'"

Woods didn't take the ribbing well. "I remember him giving me the biggest death look. He told me he was very insecure about the size of his calves. He said, 'I can't grow calves.' And I was like, 'Okay, sorry!'

Tell Us: what do you think of Tiger's calves?

For more on Tiger Woods' secret double life -- including neighborhood talk about how Elin "beat his ass" over his infidelities; how Rachel Uchitel bragged doing "nasty sex stuff" with Woods and whether his $1 billion estate is at stake -- pick up the new Us Weekly today!