Getting In is a term coined in around late 2010. It is often yelled out from a distance at any two people, usually opposite genders, to imply that there is some sort of relationship between them. It is commonly used if the two people are just talking away from a group. Whenever the phrase is said, considerable annoyance is caused to the two people, especially if one was actually trying to get in with the other.
It can also be used when a couple are hugging, holding hands or a similar activity.