Son laughing at inappropriate moments

So my oldest is 9 he has a mild form of autism followed by ADHD. When I get something on my shirt he starts laughing. Like on New Years eve at the time I was still pregnant with my daughter who’s now 4 months old! Back to my point... so I made homemade cupcakes and I was putting frosting on them and some got on my shirt and he starts laughing and said “John it’s not funny” and since he was 7 he’s been doing it😒, it’s driving me crazy and he laughed yesterday too when I got sauce on my shirt. I need help ladies!!