Short answer: Yes, you will very likely be punished.
Some insight: So I feel there's a fine line between "talking shit to yourself" and "blaming yourself in a healthy way." If you fail a Tower Dive in game and say things along the lines of "BEST DIVE NA," you'll likely get a few laughs from both teams. Even saying "Ah, shit, I fucked that up. I shouldn't have done that. My bad." doesn't have to be "clean" in regards to the language (provided there is nothing graphic or extremely biased/hate speech related), as a filter is in place for those that choose to use it. However, if you start saying things about self-harm or perhaps overly toxic things (i.e. racism, sexism, homophobia, etc.) you'll likely be punished due to the system flagging you for Hate Speech or something similar. You can always do your best to improve and try to encourage your teammates to do the same without flaming them, however when flaming yourself it puts people in a very awkward position and welcomes other people to begin badgering you: Which can lead to them being punished - even if you are okay with it. Asking your teammates to wait 10 seconds while you run from Red Buff to Mid Lane to assist them likely isn't flaming, however if you spam "?" Pings and start with "OMG WTF R U DOIN M8" it probably won't end very well for either of you as your teammates can be discouraged due to your flame, and you are now concentrated on their mistake and response rather than what you could have done to make a better situation out of it.