Two partners would have to be completely at ease with each other to hold opposing political views yet still be able to tease each other about it.
But that is just what tennis professionals Peng Shuai of China and Chinese Taipei's Hsieh Su-wei are.
Dubbed the "Cross-Straits Duo", the pair are successful partners on court - they have the most titles on the Women's Tennis Association Tour this year - and candid friends off it.
"Just don't attack us," Hsieh bantered to her partner. "If you do, I might not be able to live any more and there would be no more friendship between us."
Taiwan and China have remained technically at war since the island split from the mainland in 1949 at the end of a civil war. Beijing regards Taiwan as part of its territory, even though tensions have eased in recent years.
"The relationship (between China and Taiwan) is a special one," Hsieh said - until Peng jumped in, jokingly correcting her partner for not saying "mainland" instead.
Second seeds at the ongoing WTA Championships, the pair earned their first appearance at the year-end tournament after a successful season in which they won four titles, including Wimbledon. They play Nadia Petrova and Katarina Srebotnik today in the semi-finals.
But despite being friends and partners since their junior days, and sharing things from clothes to unusual traits like playing two-handed off both sides, the 27-year-olds admit they were not always a good team.
"We played a lot together when we were juniors but there was a period of seven years between that and turning pro when we split up," said Peng, explaining that disagreements and arguments got in the way.