This is likely somewhat hypocritical, but:
I would immensely appreciate a heads-up in a PM that my posting style was off-putting, so that I might correct it and (theoretically) receive more replies.
I don’t think I could bring myself to do so to someone else, therefore I’d do nothing.
If I can’t easily follow a post, I ignore it. As much as the grammar cop in me wants to correct really obvious mistakes in posts/replies sometimes, I restrain myself, because I’ve seen some replies on here that try to be humorous, but come off incredibly condescending. What comprises "easily followed" changes on the day and my mood, too, so I might find myself willing to try to puzzle it out the next day, if I’ve previously skipped it. Text-speak is right out—I’ve no desire to translate, but egregious and plentiful spelling/grammatical errors bother me more some days than others.
That said, if there is an obvious mistake that causes confusion in the post, I don’t see why asking for clarification/correction in the thread is rude or bad form.