Renji isn't a person who thinks much.
He acts on impulse and will think about his actions later. Sometimes he regrets them, sometimes he doesn't.
Rukia knows this. After being with him for longer than any human has lived, she'd have to. Sometimes it bothered her, and other times it didn't.
Like the times when he greets her with a sudden, impulsive kiss, or when she leaves for the human world, and he smothers her into a sudden, impulsive, warm embrace.
And she can tell when he thinks about his irrational actions later by the way he blushes.