You've got it backwards: this is the context. It probably wouldn't trigger a lawsuit on its own; it's the reason you'd lose that lawsuit, or have to settle on very unfavorable terms.
Look at the cases the OP mentioned. Each one has a concrete injury (getting passed over for a promotion, etc.), plus evidence suggesting that gender discrimination was the reason for the injury.
Now imagine that a well-qualified women applied for a job with this startup, and was passed over. Given the breastaurant photo, it would look very plausible that the applicant wasn't hired because the founders hire people they like, and they like guys they can see themselves hanging out with at places like this.
Look at the cases the OP mentioned. Each one has a concrete injury (getting passed over for a promotion, etc.), plus evidence suggesting that gender discrimination was the reason for the injury.
Now imagine that a well-qualified women applied for a job with this startup, and was passed over. Given the breastaurant photo, it would look very plausible that the applicant wasn't hired because the founders hire people they like, and they like guys they can see themselves hanging out with at places like this.