The "anniversary" that your significant other decides to celebrate every month you are together and you really don't remember (or don't care) what number month it is. Especially since you have been dating for less than a year.
As in:
"Can't go out this Friday. My girl is celebrating our whatever-versary and wants to spend time with me."
"Oh dude, how long have you been going out?"
"Don't know. Just whatever"
11👍 5👎