Twenty Percent Too Much?

Sometimes when I tip, I feel like twenty percent is too much. I hate to admit it but I guess I have a chintzy side. This guy though-- he knows how to leave a tip:

CHICAGO (Reuters) - As tips go, Chicago limousine driver Abdul Faraj got a priceless one this week when one of his regular customers offered up a kidney, media reports said.
Faraj and Minnesota businessman Dave Baker underwent transplant surgeries at Chicago's Northwestern Memorial Hospital.
"He gave me part of his body. He saved my life," Faraj, a diabetes sufferer whose kidneys were failing despite a three-times-a-week dialysis regime, told area television stations.
Baker has used Faraj, a native of Lebanon, as his driver on trips to Chicago for several years. Making small talk months ago, Baker learned of Faraj's poor health and struggle to find a kidney donor with a matching blood type.
"At that time, he tells me, 'What's your blood type?' I tell him O-positive," Faraj said. "He said, 'I'm 0-positive. I'll give you one.'"
Baker is out of the hospital and expected to fully recover within weeks.
"This was an opportunity to stop, slow down, take a look around and try to help someone," Baker told local television.