I use humor to snap myself out of a self-pity funk too. I'll tell myself "Don't do the borderline!" or "stop going all borderline over this." That kind of makes me realize I'm thinking with my emotions and it reminds me to write down the reality of the situation...the cold, hard facts. My emotions almost NEVER match the facts.
Example: (my thought) "My daughter-in-law is keeping me away from my grandson! Her mother sees him all the time, but when we come in to town to visit, she doesn't go out of her way to make sure I can see him!!!! She wants to keep him from us! I just know it!" (emotional garbage/borderline crap)
The reality: Her mother lives near her and I live in the next state. Grandson will NOT be as close to me because we live far apart. It's pretty hard for her to go out of her way to make sure he sees me when he naps, is on a feeding schedule, and doesn't know who I am so he isn't that friendly. This is just reality. The emotional "poor-me" and "bad her" is just that...emotional garbage. It's a borderline painting daughter-in-law as "all bad." And it's nonsense. She is neither all good or all bad. She is, like most, in the gray area.
My daughter-in-law is difficult as is my son, who I think is antisocial. That is also a fact. I can be difficult too, but I actually DO have the ability to use the skills I've learned to be accepting. I have done very well recently. I give credit to DBT therapy, but also pat myself on the back a bit for reaching out for help when I think I might "do the borderline." We have a lifelong disability, like a diabetic, but we CAN do a lot to control it. And we can be proud of ourselves when we are victorious.
I hope this makes sense. Like most borderlines, I can ramble!