Apologize profusely, but only after 5 minutes of being late.
This is a crucial step in the process, as it allows your coworkers to feel slightly less terrible about their lives.
Justifying Lateness is an advanced technique that requires a PhD in Apology-Fu.
The most effective excuses include, but are not limited to:
Abusive Excuses is a dark art that should only be practiced by the most experienced latecomers.
Blame others, but not too much. It's a fine line.
Use phrases like "it's not my fault" or "I was framed" to deflect attention from your own incompetence.
Blame-Shifting 101 is a free online course.
Remember, it's all about maintaining a healthy work-life balance... of guilt and regret.