We have no idea why this guy is like this. He starts by complimenting a woman’s clothing, but when she doesn’t respond in 16 seconds, he flips the script and calls her stupid. Fast-forward 45 minutes later, and he apologizes for calling her stupid. This may be a sign of an underlying problem that this “nice guy” really needs to resolve.
Sliding into someone’s DMs isn’t an invitation to engage in conversation. They’re always within their right to respond or leave you on read. If you don’t get a response, just ignore the person and continue with your day. Don’t let her lack of response ruin your day, dude.