Twitter Inc. can't seem to go more than a week without a belly flop. 

The company's top priority is adding users, but it hasn't lured many of them. Revenue shifted from perky to pokey. One potential buyer after another ran screaming from the deal table. Twitter fired 9 percent of its staff as it tries to change the conversation from its disappearing growth to potential profits. 

And now one of the key grown-ups at Twitter is heading for the exits. Adam Bain, the operating chief and longtime head of advertising sales -- the only part of Twitter that was functional (for a while) -- is stepping down after six years to "explore opportunities outside the company."

It's hard not to wonder if Bain stuck around through a revolving door of Twitter CEOs over the years only to give up after the recent layoffs hit his advertising team hard. Twitter declined to offer revenue forecasts for the current quarter because the job cuts and an overhaul of the ad sales staff made it too tough to predict the business. It's only one quarter of unpredictability, but it shows how tinkering with the company's revenue engine has an uncertain effect on sales. 

Regardless of the reason for Bain's departure, Twitter is already a joke for how often it cycles through senior executives. This merely adds to the punchline. It makes the company that can seemingly do nothing right look even more dysfunctional.

In response, Twitter's shares fell about 3 percent in after-hours trading after they had closed higher in the regular market day on Wednesday.

Twitter said Anthony Noto, the company's powerful chief financial officer, is sliding into Bain's COO job and will give up the CFO post once Twitter finds a qualified successor. It's an interesting job swap, although it reflects Noto's expansive responsibilities at the company. 1 CEO Jack Dorsey is more of a spiritual leader and strategy guru rather than a day-to-day executive functionary. With Bain gone, Twitter needs to lean even more on Noto. It's Noto or bust. 

As Twitter's executive suite hollows out more, it seems even more odd that Dorsey continues to hold two CEO posts, at Twitter and Square Inc. I've called for Dorsey to pick one; Twitter is simply too bruised and battered to have a distracted part-time chief executive.

The Twitter board apparently continues to back Dorsey and isn't forcing him to pick between jobs. The news of another fleeing executive raises the question of whether Dorsey still has the support of his Twitter colleagues. 

1. It's possible Noto's ambitions simply couldn't be contained by his existing job title, and Bain was in his way. Twitter headquarters contain more drama than Hamlet. 

To contact the author of this story:
Shira Ovide in New York at sovide@bloomberg.net

To contact the editor responsible for this story:
Daniel Niemi at dniemi1@bloomberg.net