I almost don’t want to talk about intentional mistakes because the whole area is a gigantic grey blob. Sometimes it works, and sometimes it doesn't. You have to be careful and use your own discretion, but here’s one way I feel it does work:
“Me and Kelsey...”
I’ve had this phrasing in my novel for a while, but it’s finally been pointed out by a critic. I expected it to raise alarm bells for many more writers than it has because the critic was right. It isn’t grammatically correct...
It is a deliberate mistake. In a normal conversation with my friends, I don’t think I’ve ever actually said ‘Kelsey and I...’ because it sounds too posh – and I’m from Oxford! Instead I worded it how I felt my character would have said the phrase in that situation.
Conversations are imperfect, filled with false starts, grammatical errors, and ambiguous phrases which are nevertheless understood perfectly fine at the time. If you write dialogue the way you actually speak, it would be very confusing to read. The idea is to capture that imperfect feel whilst still making sense, keeping in mind the way your character talks and thinks.