This is not a common saying (Seems like I just heard it, though -- was it in "Breaking Bad?"), based on the (obviously flawed) stereotype some Americans have that Arabic people are terrorists, hence might be subject to more scrutiny by law enforcement than a Caucasian would while trying to enter the US, making them nervous and sweaty. Here, it's a comparison, meaning whoever he is talking about is really really sweaty -- covered with perspiration.