There's no such thing as "bad" bitcoins. The bitcoin network was built to be censorship resistant.

There are, however, things such as bad exchanges.

These are the exchanges that, for whatever reason, determine your deposit consists of mixed coins and hassle you. So if you are concerned, just don't use these coins with a custodial, centralized exchange. There are many methods where you can trade those "bad coins" where chain analysis is not performed and they are KYC-free (e.g., Bisq, HodlHodl, LocalCryptos, LocalCoinSwap, etc.), numerous swap services, or spending at a merchant that would likely not perform chain analysis. Same for merchants -- most do not perform on-chain analysis, except for those that use a merchant payment processor and it is those payment processors that may perform the on-chain analysis.

Or you can do a CoinJoin (e.g., with JoinMarket) which helps to ensure that you have financial privacy when you spend.