Are girls comfortable with it? Well, depends...if you are kissing a lesbian, I suspect the answer would be "no."

But seriously, the answer is "It depends." If you are just giving her the first kiss, the peck on the lips...well, an erection is a bit creepy at that point. If you are beginning French kissing her and getting steamy...well, at that point, the bigger the bulge, the better...gets her attention that you are a man and that you are a man and that you are a man. Like, duh?!