How do you discipline a child that just laughs when you tell them off?

[RedK2000]

I have just caught my 6 year old DD pretending to wash her hands, stood at the sink, tap running singing happy birthday pretending to wash her hands. This has been a recurring problem for years. 2 months ago she had worms, we told her it was worms and explained again how important hand washing is. Now with covid she knows another important reason to wash hands, yet still pretends.
I sat her down to say how disappointed I was and how important it is not to spread germs. She just messed about and laughed. I put her in time out. She messed around. I was going to take toys off her, but there's nothing she's really bothered about. She just doesn't react to me being cross, annoyed, disappointed she acts daft, defiant and laughs at me. Yet in all other areas of life shows empathy, common sense and concern for others. But on hand washing and being told off she acts like this.
What can I do?

Perhaps explore the reasons why she doesn’t want to wash her hands? She is actively not washing her hands and it probably requires more effort to pretend to wash them so it’s not laziness. I suspect it’s a sensory issue. I have sensory issues and I can’t stand the feel of water, I hate getting wet. Obviously as an adult I’ve learnt to deal with it and I do wash my hands but it was a big problem as a child.

As others have said I also think the inappropriate laughing could be a stress/anxiety response. I do this too.

My 9yo (still) isn’t reliable on brushing her teeth. When I catch her not doing it )and I do spot check), I do several weeks of her having to be supervised whilst brushing.

It’s inconvenient for both of us, but it’s important, so I do it. At some point, it will be ingrained enough that she will do it herself. Until then, I supervise. I think you need to take the same approach.

Does she see you wash your hands? Maybe wash your hands at the same time with her and help her.
When my son has a repeatedly unhelpful behaviour I see what I can do to model a better way.

The hand washing is not an option "if you dont you cannot snack" yes but it isnt about options to snack or not . It s what she has to do.
It s a necessity not optional. So you take her and supervise.

@RedK2000
This is commonplace for my lo who's on the asd spectrum.
It's difficult and generally I have to repeatedly explain why I am disappointed or this action has shown I cannot trust them etc, eventually that rote element sinks in, but the social anxiety element which causes the smiling and laughing due to not knowing how to process the emotions is still there. And that's hard...

I remember being in secondary school about to start an experiment and the class slacker tried to delay the class, come in late and then pretend to wash her hands. It delayed the teacher and the rest of the class. Little did she know that the experiment was growing bacteria and she was asked to prove how clean her hands were by letting the teacher swab her hand and grow the bacteria. After a few days it was suitably disgusting and I’ve washed my hands thoroughly ever since.

Could you do a version of this experiment in a more positive way with your daughter?

I used to do "thinking time". It's the same as time out but they're supposed to use the time to think about what they did, why they did it and the consequences for themselves and others. Then when time's up they have to tell me what they've been thinking.

Sometimes I got to hear some interesting insights, mostly I didn't but the whole process was so uncomfortable for them, that they avoided getting "put into thinking time" more than they disliked time out.

I would look at why she isn't washing her hands. As a child I would do the same thing - pretend to wash my hands - I had (and still have to some extent) sensory issues around the texture and fragrance of things like liquid soap. Unfragranced bar soap was tolerable but other types would make me gip, and on occasion throw up.

Sounds like my DD. I sometimes wonder if she is a psychopath. We have fights about baths. I think she likes being dirty. We fight about everything. Lockdown exacerbates it all. She says she is like this because she is comfortable being herself around me. She probably says that to draw me in to thinking she's the sweetest angel there ever was before she stomps all over me again.

I find conversations when she is in the right frame of mind and bribery work the best.