Star Trek: 10 Things You Didn't Know About Miles O'Brien
9. The Pip Thing
One of the long-running sight gags - unintentional though it was - was the confusion of what exactly O'Brien's rank was on any given week. Though an enlisted man, therefore not holding an officer's rank, O'Brien is frequently seen with the pips that adorn the collars of the officers on the ship and the station.
First, he was given an ensign's pip in Encounter At Farpoint. Several episodes later, swapped already to Operations Gold, he wears no rank pins at all. Following this appearance, he would wear the two gold pips of a lieutenant for quite some time. It was Ronald D. Moore who came up with the idea, despite previous episodes referring to him as 'Chief', with making him a non-commissioned officer when Worf's adoptive parents boarded the ship in Family.
O'Brien was originally just a day player on TNG and very little, if any, thought went into his rank or background for quite a while. He officially became a Chief Petty Officer in "Family" when I wanted he and Worf's adoptive father to both be non-coms in contrast to Worf. Making him an enlisted man seemed to give us another color in the show and to open up another window into Starfleet that we hadn't explored before.
Star Trek: Lower Decks would poke fun at the irregularity of rank pips in Kayshon, His Eyes Open, explaining that whenever someone appeared to have additional rank pips, it was just because they were eating delicious street corn. Because of course!