Dreams about uninvited situations, especially at social events like birthday parties, often reflect feelings of exclusion or anxiety about social acceptance. The fact that you were driving an unknown person could symbolize a journey or direction in life that involves others, perhaps hinting at new relationships or changes.

Not wearing underwear in the dream suggests vulnerability or a sense of exposure. It could indicate that you feel unprepared or insecure in certain social situations. The t-shirt may represent a desire to keep things simple or casual but also a lack of complete readiness for the environment you find yourself in.

Your cousin being the host, despite not having a relationship with them, might signify unresolved feelings or tensions within your family dynamics. Leaving the party after being asked to stay could indicate a desire to escape uncomfortable situations or confrontations in real life.

Overall, this dream may be urging you to reflect on your feelings about social interactions and how you relate to family or unresolved issues. It could be beneficial to explore these feelings further and consider if there are any steps you would like to take to address them.