I can see Steve less willing to do that with mundanes post-serum because he knows he's a lot stronger than Joe Average and might actually hurt someone seriously if he's not careful. Pre-serum Steve was more likely to hurt himself, and that was a risk he was comfortable with (even if it probably annoyed the piss out of Bucky).
Also, now Steve's Captain America so 'he probably won't hit me, but if he does, it'll hurt' might add to the effect of Strong Words and Disapproval.