I check the person's forehead....
What do you say when people ask how good at chess you are ?

With good reason, no one has ever asked me how "good" at chess I am.
Hmm. I have been asked quite often. Usually, it's when people see a chess set or chess book at my home, which is common since I don't usually put them away.

I say I play a little, online, whenever I want to avoid doing housework.... but, then, I'm stuck with having to admit that I play a lot.

your a fun chess.com personality, inlaw. I don't believe you play chess just to get out of housework.
you should say gosh, I'm pretty darn strong.
after all if THEY were strong, would they ask? no. strong players respect the game too much to ask "glib" questions.

In the spirit of being honest, I tell them that I am the reigning Troll Chess Champion of the world.
https://www.chess.com/forum/view/tournaments/1st-troll-chess-championship-macer75-vs-computer2-medium

I tell them that I used to be OK at it.
IIRC, my peak OTB published rating was a bit over 2050. Peak performance rating (single event) about 125 points higher.

Better than I was yesterday, worse than I'll be tomorrow.
There used to be a Russian saying: "Life is getting better every day! Well... not better than yesterday, but certainly better than tomorrow!"

"Pretty good, but no expert."
That doesn't work for me, though. I'm pretty bad, but I am an Expert.
Expert rating is 2000 - 2199

I usually say compared to Bobby Fischer I'm not that good, but compared to an onion I'm a very decent player.

"Pretty good, but no expert."
That doesn't work for me, though. I'm pretty bad, but I am an Expert.
Expert rating is 2000 - 2199
As xMillsy saId, "I am nothing exceptional by any means."
I just tell the asker exactly what my rating is or I just say I am not very good
at chess, which is true. But what defines"not very good at chess?
In the US, if you say "I play chess a little", it means you know how the pieces move. In Russia, if you say the same thing it means that you're at least 1800 strength.