Trump claims it's because he didn't wait his turn.

Donald Trump removed Univision reporter and Mexican-American Jorge Ramos from his press conference last night in Iowa. Trump claimed it was because Ramos did not wait to be called on, which didn't sit well with the other reporters because that's not how press conferences work. Reporters have to be aggressive to ensure they're seen and heard, and Trump's instant remark that Ramos should "go back to Univision" indicated that he knew exactly who Ramos was and simply wished not to speak with him.

Sources: CNN Money