Clark can still feel Bruce shifting under his hands, trying to coax him into going faster, which is definitely not happening. He just makes a small noise of agreement as he drags his tongue up, slowly, slowly, just to hear Bruce's low groan.
When Bruce goes still enough that Clark thinks he won't get tetchy again, Clark lifts a hand from his hip, curling it around the base of his erection and stroking him with the same inexorable slowness with which he's approached the rest of this morning. Bruce's breath stutters in his throat; his body coils tight beneath Clark's hand, then relaxes, muscle by muscle, as he lets out a quiet sigh. He doesn't grouse any further, though, which Clark counts as a victory.
When Clark hears the bedframe creak from Bruce's grip, he glances up, and—okay, it's a little hard (difficult, difficult) to say no to the raw want in that expression. It's difficult to resist in the face of Bruce wanting him even when Clark is braced against it, but here and now, with the walls broken down from between them and Bruce spread out before him, hard and wanting and bound only by his own will.... Even Superman has his limits.
So Clark shifts, adjusting the angle of his neck, and takes Bruce properly into his mouth. Bruce rewards him with a breathless, muted moan. Clark's other hand wanders, tracing the planes of Bruce's abdomen, his ribs, his chest—and Bruce is quick to utilize his sudden freedom to roll his hips, moving up into Clark's mouth almost languidly in contrast to how impatient he's been so far. Clark does his best to move at Bruce's rhythm, stroking and bobbing his head in a gradual drag, coming close to but never quite pulling off of him entirely with every motion. His tongue drags along the underside of Bruce's shaft, laps around the head when he draws back, but Bruce saves those shuddering, desperate sounds for when Clark's tongue laps at the slit, or when he hollows his cheeks to suck, just so.
The rush of Bruce's heart, the faint tremble in his breaths—God, it all washes over Clark like a tide, and it takes a nigh herculean amount of effort not to take a hand off of Bruce to touch himself in turn. Right now, he wants to see how much he can love on Bruce until he's a groaning mess under Clark's tongue.
"Clark," Bruce breathes, "please..."
Which, if he keeps this up, might be sooner rather than later.
Clark moans softly—and Bruce seems to like that pretty well too, judging by the way he shudders. He pulls off of Bruce with a soft sound, still stroking him while his other hand takes hold of Bruce's hip again, lifting him slightly off the bed (and he definitely likes that, likes those little reminders of how easily Clark can manhandle him) to make it easier when he cranes his neck down to put his mouth on Bruce's balls, drawn up tight to his body. He's close, or getting there, and Clark is tempted to pull back, to draw this out—but he thinks Bruce might seriously kick him then. His body is coiled, tense, his heart a thundering drum in Clark's ears, and the keen awareness that it's just Bruce's own stubbornness keeping him from reaching down, from gripping Clark's hair and yanking him back is enough to make Clark want to do it himself, drawing Bruce back into his mouth, stroking and sucking him barely out of rhythm with Bruce's heartbeat.
Bruce's thighs tense, the motion of his hips turning frantic and erratic. "Clark," he gasps, jerking up once, twice, and that's all the warning Clark gets before Bruce is coming down his throat.
Clark pulls back to avoid choking, and Bruce catches his cheek, his chin. Bruce's eyes are closed, his lips parted as he draws in deep, ragged breaths to bring himself down. His Adam's apple bobs, a tiny rivulet of sweat darting down the column of his throat. Pausing to wipe his cheek with the back of his hand, Clark climbs back up Bruce's body, kisses him and swallowing the tiny, overwhelmed sounds Bruce makes into his mouth—either at the events of the morning or at the taste of himself on Clark's tongue, it's difficult to tell.
Bruce's self-control finally breaks then, his hands wasting no time tangling in Clark's hair and holding him right where he is. Clark's definitely not about to complain about that—or about the way Bruce licks his way into his mouth, God.
"You planning on making a habit of that, Clark?" Bruce asks, his voice still low and rough (and Clark knows he probably shouldn't be turned on by how close it is to the Bat's voice, but the dick wants what it wants). "Because I really don't want to die of old age waiting for you to bring me off."
Clark chuckles, settling himself so that he's sitting astride Bruce's hips. "Only when you have time to spare," he promises.
Bruce rolls his eyes. "Clearly I need to schedule more morning meetings," he says, but he's cracking that crooked little grin when Clark leans in to kiss him again.
One of Bruce's hands trails down from Clark's hair, to trace Clark's shoulders, his ribs, his hip—oh. Clark gasps against Bruce's mouth, unable to keep himself from jerking up into Bruce's fist. That grin against Clark's lips sharpens into a knife's edge; Bruce's other hand finds Clark's hip, gripping him hard enough to bruise anyone else before the whole world upends itself and Clark is on his back before he even has the chance to yelp.
"Turnabout's fair play, farmboy," Bruce murmurs, "don't you think?"
If Bruce thinks Clark is going to mope about this—having Bruce leaning over him, broad chest still heaving, heart still pounding, the glint in his eye nearly predatory as he grips Clark's wrists and pins them to the mattress with one hand—he's going to be sorely disappointed. Bruce trails his free hand down Clark's chest, his eyes following the path of his fingers almost appraisingly. He looks back up into Clark's eyes, and his smirk is no sharper than that crooked grin as he jerks Clark's hands up, dragging him into a sitting position, and Clark just goes along with it, as if he couldn't just put Bruce on his back again if he actually wanted to (which he really, really doesn't). In the dwindling part of Clark's brain still capable of coherent thought he muses that this is a little poetic, isn't it, before Bruce presses his wrists against the bedframe and—and reaches for his nightstand, yanking a necktie off the lamp.
...
Well then. Turnabout indeed.

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I'm hoooping to have this wrap up in another 3 or so posts. Seeing as OP mentioned both sides of the coin being pretty great... I had to agree. :^D P.S. Thank you for this particular prompt, OP; I swear it was specifically created in a lab to get me crawling out of the woodwork to write stuff instead of internally gushing over how good everyone else here is.