The Deleted Answer:
The Interpersonal Skill here is Setting Boundaries. Note though that you don't specifically need to express them.
It seems based on your description that while they're pals, they're not confidants*. Meaning if you mention this, they'll probably just blame the apt for being too small and you're just whining.
The boundaries you set are just meant to make sure you're not put out, left out or inconvenienced based on their actions.
How to set boundaries: If they're late, leave without them. Always have your own ride home. Meet them at the location/venue. Don't cover more than 5$/£/€ or whatever amount you can let go.
Basically, don't put yourself in a position where you are depending on them.
Making them your friends of convenience will at least balance the relationship.
For clarity, my position is that talking about this won't accomplish much if anything so don't bother. You won't change them but you can change the relationship.
I think this complies 100% complies with the Rules:
Aim to provide expertise, not an opinion: The expertise if from experience. Very few Answers lay any specific expert foundation because it's often just not necessary. Beginning every Answer with "I know how you feel" is technically complying, but almost always superfluous.
Try to avoid writing duplicate answers: I'm quite sure this was the first Answer.
Your answer should be about the interpersonal skills needed to solve the situation: I specifically call out the Interpersonal Skill, Setting Boundaries, then give examples of how to set boundaries. I even highlight this passage after a Comment.
Respect the request of the person asking the question and answer the actual question: OP specifically highlighted what they were looking for:
I want to address this behavior and clarifying it was definitly not okay.
Since this is specific on two parts, I took this as the primary question over the Subject question. I specifically answer both parts, "address this behavior" is the main points of the Answer. I chose to address the "clarifying" part as unnecessary and provided a specific reason.
I must point out that "address" does not necessarily mean talking. There are many way to address a situation that do not involve words.
Then what about those 'frame challenges': This Answer did not contain a Frame Challenge.
Take note of possible cultural differences: There were no significant cultural differences to consider.
Make clear which specifics of the question are affecting the answer you give: I suppose I could have referred to this:
But I just don't want to loose them as friends, because if things work out we always have a ton of fun.
As the reason to set personal boundaries and not confront them. But since OP made this point specifically, I didn't think it was necessary and would have been redundant.