Notice the upcoming composition, and then quickly take it.

Oh yes, the speed helps a lot! Not to be so obvious. Shoot and pretend nothing happened :D

And with time as you grow more comfortable, the less you even think of this stuff, you're so in that zone, the flow of noticing and capturing, that you have no problems photographing people and thinking of whether they notice or not.

Something I look forward to :)
And yes, it does seem people generally dont mind. I just have to get more comfortable with it.