Natasha hated shopping. Especially at food stores. She never went alone if she could help it. She despised the crowds, the high prices, the screaming kids, the small spaces, everything. When she would go out and try to find something edible to eat for her, Clint, and Coulson at the safe house, she would try her best not to knock out all of the idiots large food stores tend to attract. Once, she nearly blew her cover by desperately wanting to murder a man who rammed into her with a shopping cart, knocking her items astray. She exercised extreme self control, put on a bright (fake) smile and preceded to apologize profusely for being in the man's way.
When she was lucky enough, Clint would come with her. She didn't understand how he could be so patient, so comfortable, and so nice to all of the unaware idiots strolling through the store. If someone flew by with their cart, he would move quickly out of the way, taking great care in making sure he didn't harm anyone as he cleared the path. If someone pulled unknowingly out into the isle, he would wait patiently for them to move slowly out of his way. If someone cut in front of him in line, he wouldn't say a word, just smile slyly, watching the red head go red. She didn't know how he did it.
Clint thought it was hilarious the way Natasha acted in stores. She would glare at everyone with an icy gaze, giving off the impression that she wanted to kill you with her eyes. When something happened, say, someone accidentally bumped into them, Clint would watch in amusement as Natasha's hand would creep slowly down her leg where her knife was hidden. Clint would smile warmly at the person, and then move on, going for items away from people so Natasha wasn't tempted to go on a killing spree.
Once, in a Wal-Mart in Ohio, she voiced her thoughts on the archer's actions. Clint, who was pulling things off the shelves according to the list Coulson had made, laughed when she asked him how he didn't rip out the throats of every single person in the building. He threw a bag of chips into the cart then turned to her. "It's because I know I can," he said, before turning back to his list.
The next mission they went on, Natasha took to the store herself. Clint had offered to go, but Natasha declined. When she returned two hours later to the safe house, laden with all of their supplies, Clint rushed outside to help with the bags, and to ask her how it went.
She smiled, then said "Every time someone annoyed me, I imagined pulling out my knife, and, ah, practicing my aim."
Coulson, who had slipped outside upon her return, knew nothing of Natasha's hatred of stores. He glanced up.
"What was that, Agent Romanoff?"
Natasha and Clint shared a look, then ducked inside, laughing silently to themselves.