Steve wasn't entirely sure what he was thinking. In fact, he was fairly certain he wasn't thinking. But his confrontation with Black Cat had left him rather...perhaps flustered was the word for it? Hot and Bothered?
It wasn't so much who was in front of him as that there was a body, a willing (surprisingly willing) body, who would get rid of these feelings. Tony was his buddy. Buddies helped each other out. There had been a term passed about in the war, 'what happens in the trenches stays in the trenches'.
It wasn't a calculated manipulation.
His lips quirked slightly at the challenge, the kiss becoming something of a fight for dominance at that point, lips parting and a hand gripping the back of Tony's neck to hold him still.