Are we crazy? Is this normal? My girlfriend and I have an imaginary friend. His name is Toby and this has been going on for about 4-5 months. Are we alone or do others do this as well??? Redditors, your thoughts?

My girlfriend and I have been living together a little under a year now and about 4-5 months ago, we started to include an imaginary friend into our lives who we dubbed as Toby. Here's how it (Toby) began... We started to joke around about Toby after watching Paranormal Activity 3 (the demon or ghost in the film is named Toby). FYI we are not satanic worshipers. Silly as it sounds, we started to mention Toby's name and we included him in our conversations when we misplaced something, or if we forgot to commit to a chore, or if we made a mistake. We just started blaming Toby for all the little things. (e.g., I'd ask my GF "Did you leave the light on this entire time?" She would retort, "No, Toby did it" Then I'd add, "Toby knows better than to leave the light on") This would go on for a few minutes and most of it is trivial. Sometimes we'll get into small arguments because I'll on occasion, threaten that I'll beat Toby up. Then my GF gets upset because she thinks if/when we have kids, that I'll do the same. I'm harmless and really joking but, this happens almost everyday. Is it weird? Is this some defense mechanism we're doing as a couple? I'm just wondering if anybody else does this (not crazy folks). Any Redditors do the same? This is my first Reddit post btw.