If the New Orleans Saints had just-so-happened to pick Mark Ingram in the 2011 NFL Draft, it might have been one thing. But they went out of their way to do it, trading into the first round after using their first pick on Cameron Jordan specifically to get the former Heisman Trophy winner, which left the Saints' three active running backs, Reggie Bush, Chris Ivory, and Pierre Thomas, in a strange place, to say the least. Reggie Bush was the first and most fatalistic to respond, tweeting "It's been fun New Orleans" after the pick was made.
Since then Bush has backpedaled a bit, although he hasn't deleted the original tweet; three hours later he added some conciliatory congratulations to Mark Ingram, saying he'll be a "great addition" to the Saints backfield, although he doesn't say anything about whether he thinks he'll be subtracted.
Bush has always identified strongly with his adopted hometown of New Orleans, and New Orleans, in spite of his pro setbacks, has responded pretty fondly. It's no surprise that he'd take a possible ouster from the Saints personally.