I've done over 15 years of Martial Arts Training, but it didn't stop my ex from knocking me out once. 

I was teaching my ex how to punch and kick to defend herself should she ever need it!  Needless to say that afternoon, we had a big disagreement, and I saw the most perfectly executed right hook from her land on my chin.

I just remember coming around to barrage of apologies.  My friends that used to come to my house used to laugh at me when I said I'd been knocked out by her as she looks quite petite.  They soon stop laughing after I told them a she's also a body pump (weight lifting) instructor and would be downstairs shortly.

True story, although I can't say it helped our relationship any.  It just made me flinch everytime we had an argument and she made a sudden movement.   LOL