The phrase often suggests that someone is present without an explicit invitation.

Uninvited Guest

Used primarily in casual contexts, not formal or professional settings.

Casual Occasions

Implies physically going somewhere with someone else, rather than participating in an activity.

Sometimes used to express annoyance when someone's presence is not desired.

Can suggest that the person isn't contributing or is out of place in the setting.

Can carry a sense of loneliness for the person trying to tag along.