Vulgarities? fuck that. You should be able to say anything about a president, prime minister, king, queen, el presidente, or their policies that you want, in any manner you choose to do it. They can choose to ignore you, or personally make a plea that you not act like a complete ponce, but should the government crack down on you? No. Being a Ponce isn't illegal, and if thinking obama is a prick makes you a threat to national security, there are millions of americans who think the same thing, and they may actually be within spitting distance of the president.
It's just a slippery slope.