There's a difference between being pleasant to folks whom you're not fond of and being no-bullshit. The former is a matter of social protocol. The latter means that you don't go out of your way to schmooze and engage in meaningless conversation.

As an example, I can't imagine you going out of your way to ask your cow-irkers about their kids, what they did last weekend, etc. unless you were in a situation with them (in the lunch room, or waiting for a meeting, etc.) where such protocol was the norm.

Americans think if you're not actively engaging them on a social level, you're unfriendly.