Louis Tomlinson feuded with Zayn Malik.
They feuded not just once, but TWICE on Twitter. At one point, Zayn got involved with a feud that started between Louis and Naughty Boy when he tweeted, "remember when you had a life and stopped making [expletive] comments about mine?"
And on another occasion, Louis jumped in to defend Calvin Harris when things got heated between him and Zayn. He actually favorited one of Calvin's tweets while they were feuding!