Granted, I have never personally been pepper sprayed or sued. I have been slapped for kissing a girl, but never when it was clear (to me) that she was uncomfortable with my advances. I never tried to kiss a girl, for example, before at least having had a successful date. I got slapped once on a 3rd date only to learn she had a great time but didn't plan to kiss a guy until her wedding day, so she was pissed I ruined that. Of course, she never shared that with me, and it was the 3rd date. Worst part was, once I learned that was her rule, I knew for certain I didn't want to go out again.
She could've told me at the outset about her atypical rule and saved us both a lot of time. I would never have gone out with her at all had I known. What dude wants to marry a chick he's never kissed? What if you get to the altar, exchange rings, and then realize for the first time that you have no physical chemistry at all? Talk about bad news. I'm not saying you need to "go all the way" before getting married, but never even kissing before marrying? I can't work with that restriction. Also, she gave me every indication she was into me. And she was. She just didn't want to kiss me. Or, rather, she did, but she didn't want to do it until we were getting hitched, which was also weird - she's imagining getting married on date 3, and I am out of line for wanting a kiss? Who was really rushing things...
Another girl slapped me HARD, and then apologized saying, "Oh, no - I didn't mean that it was just a reflex I swear." With reflexes like that, imagine the wedding night? I ain't no John Bobbit. She actually was fine with being kissed, but she left a hand print on my face because I surprised her. She made up for it by getting me ice, and she kissed me while holding the ice pack on. I was shocked.
On the occasions I asked, like Oni, I have also had girls tell me that they would have been fine if I just did it but that the moment was lost. That was why I came up with the whole just tell them and then swoop in. I have found that this gives them warning as previously pointed out, but on one occasion the warning was used to prepare a slap.
Bottom line: if you date enough as a guy, then you will probably get slapped sooner or later, even if by accidental reflex. I have had friends who got pepper-sprayed, and I have to think my warning technique (used for first kisses only) probably saved me from that. I had one friend who got reported to campus police for kissing a girl. Fortunately, she didn't falsely accuse him of something else, but there was an investigation, and his entire dorm went through "training" by university (campus life) staff members. Ironically the cop thought making the report was an "overreaction" since it was one kiss, and the guy never did it again after she told him it was not well received.
All of the above are minority horror stories, though - like less than 10%. Most of the time when I dared to lean in for a kiss, it was well received. In those few cases where I had misjudged, most ladies were cool enough to just politely tell me I had misread their feelings, which I appreciate in comparison to slaps and more severe alternatives.
I have been professionally involved (not as a party or defendant) in several court cases, though, that have caused me to warn most guys about the risks you take just trying to be romantic. I've even seen a case where a guy was accused of stalking for having flowers delivered to a girl he liked. He had asked her out a couple of times politely but unsuccessfully, and he thought sending flowers might show her that he was really serious about liking her and not looking to hurt her. She called the police, and the well-intentioned card he wrote out was tendered into evidence. It was something like, "Dear ______, I am crazy about you and hope you will reconsider going out with me." The word "crazy" on the card was used to justify a restraining order.
So, most of the time you're going to be okay, but there are risks. You can't always avoid taking risks in life, but it is good to actually be aware of them.