Yes, the "safety is for other people" approach to science had served them both... not so well, to be honest. Did either of them learn from it?

No, not really. Why else are they in this tub?

For this kiss, apparently. Bruce has enough time to register that Tony's on his way, and enough time to bring an arm up around his back to keep the waves from Tony's sudden movement from tugging them apart, then there's more sensation than calculation. He's aware of the prickle of facial hair and the occasional graze of Tony's teeth. He might not win the battle of the aggressor, but he doesn't have to; he has patience on his side, and it's a patience that could keep them in this hot tub for hours, just for the taste of Tony's mouth and the chance to wrap his arms around Tony and pull him in closer.