You know you've played too much sims when every person you meet or tries to have a conversation with you always falls on deaf ears as you try to figure out which Sim they resemble most.
You know you've played too much Sims when you start a new file in a familiar neighborhood and you know the work hours for every single sim that you plan for your sim to run into, example: In a dynasty file I got an opportunity to take a picture of Iqbal Alvi for Christopher Steal, so I sent my Sim to the library for 2 hours (it was noon Sim-time) because I knew he doesn't get off work until at least 3 and then he has to get home from the business building a couple blocks away.
On the same note, you know you've played too much Sims when you already know the birthday of all townies in the neighborhood your playing in.
You know you play too much Sims when you are going through the "Weird Pics, Funny Posts or something new" post and you can't stop laughing at something but no one around you who doesn't play sims frequently gets it.
I could do this all day! I definitely play too much Sims!
Edit to add: when you are going through the "Weird Pics, Funny Posts or Something New" forum post you can always point out Agnes and Christopher steal in unnameable screenshots. I just went to that thread and it reminded me of that.