Simple, often secret, way of saying I Love You over text or chat, without being too forward

I miss you.

Most Easy ass password that some kid will brag about in school

The first 3 numbers you learned this in kindergarten I hope you looked this up as a joke

used in web forums to denote a quote that they entirely agree with 100%. the term "you took the words right of my mouth" comes to mind.

however, because they forums disable spaming by requiring people to type at least 3 characters per post... 123 comes to mind

If someone is trying to attack you you say 123 and punch them

the numerical version of "abc".
Which means, "simple"

it is often used as a term denoting the word "numbers" or referred to counting

123 is also the first thing that comes to my mind when I hear the anything related to numbers or maths.