One face he produces would be quite unpleasant to an average bystander, but to Iris, it's nothing less than charming, even tempting in a way. She might catch him by surprise on a casual afternoon, slipping her fingers beneath the waistband of his jeans to cup him through his boxers. His eyes will initially widen in shock before catching on to her intentions. While he grinds into her grip, he might let out a naïve chuckle. Beads of sweat will probably gather at his forehead, his cheeks will scrunch awkwardly, and his mouth will purse into a dumbfounded circle. She decides he looks a little bit like a fish this way, and she smirks at the view. She fondles his bulge until the fabric at his crotch seeps, wondering if he's aware how much a clumsy grimace like that of an eager teenager suits his young face.
Contrarily, he looks the most mature (and arguably the most attractive) when he displays his face of restraint. She could be on her knees, fervently sucking him before managing a glimpse upward. If he stills his manic, speedster quivers for long enough (as they're more challenging to command than his facial muscles), she catches sight of his face, drawn so taut that she can see the shadow of facial hair growing in, lending him an appearance of vigorous masculinity. The veins in his stiff throat are prominent, bobbing while he swallows with all the discipline he can muster. His nostrils flare dangerously and his mouth presses shut. At such a point, he wouldn't dare open his eyes, knowing full well that the sight of her lips around him would shatter any guise of self-control. And they can't quite have Barry cry out in elation when they're on the floor of his lab, though this face isn't exclusive to when they're in public. Occasionally Iris witnesses it in the private confines of their sheets, in those moments he doesn't want to let her completely take over him yet. She has to admit he's become quite skilled at this one: if he ever breaks his constraint while he pulses into either her, her palm, or her mouth, it would be to release the hint of a grunt and nothing more.
Sometimes, it's just a blank stare. This is the rarest one of all. He'll seem composed, almost passive. His lips are straight, his skin flushed, but the true indicator of arousal is his eyes. They're so dark, his pupils dilated to eclipse the green of his eyes so that one might never know their true color. The thick lashes that normally brand him with innocent boyhood are suddenly a beacon of lust with the way they intensify his gaze. It's a face of desire in the purest sense. It might appear when his eyes settle on the slight bounce of her breasts as she slowly rocks her hips against his body sprawled underneath her. She used to find it unsettling that Barry Wears-His-Heart-on-His-Sleeve Allen could be reduced to such an emotionless, carnal state, but maybe it reminds her that The Flash is as human as anyone else.
She loves the untamed face that materializes when they reunite after separation by an evil, by an earth, by a timeline. In these instances, Barry abandons any pretense of inhibition or modesty in relishing her body. Iris lets him, of course, but not until she indulges in his. She too wants her hands on him to amend for being apart. And those urgent hands find his swelling length after they rub his arms, stroke his chest, graze his naval. She just wants to touch all of him before he enters her, run her palms across his every part and crevice to make sure he's really in her presence and not in a dream like he had been so many times before. She takes her time pumping him until she herself can no longer stand the agony contorting his face, so she breathes a single word in his ear: "Now." Only then does he tangle their legs together, take her upper lip between his own two, and push into her, his eyes squeezing shut. As he's dripping down her thighs, he has to break their kiss to tilt his head and drop his jaw, and in the split second before he expels the air he sucked from her, Iris believes she was made to extract this face from Barry.
Perhaps her favorite of his faces is one that isn't indicative of his pleasure at all, but rather is in awe of hers. They're thrusting frantically into each other one night, both on the verge of climax. Despite the heated rush to finish, she's aware he's holding back for her sake, and his selflessness alone almost makes her come right then. But what really gets her is the tender face he maintains as he watches her ungraceful surrender to her impulses. His eyes are soft, crinkling when the corners of his lips turn upward in a manner too sweet for the desperate passion ensuing between them. The image is what finally makes her lose it: all tension leaves her body, replaced instead with euphoria. She allows herself only a brief period of recovery to make sure she catches him finish. It's difficult to tell if the expression of blissful content Barry wears is the result of him watching her revel in pleasure or the product of him marveling that he's inside her. Whatever it may be, Iris is comforted knowing that she is the reason behind the peaceful flutter of his eyelashes and the breathless part of his smile.