aceca

Usernames are online identifiers:

https://ico.org.uk/for-organisations/uk-gdpr-guidance-and-resources/personal-information-what-is-it/what-is-personal-data/what-are-identifiers-and-related-factors/

A non-exhaustive list is included in Recital 30

An individual’s social media ‘handle’ or username, which may seem anonymous or nonsensical, is still sufficient to identify them as it uniquely identifies that individual. The username is personal data if it distinguishes one individual from another regardless of whether it is possible to link the ‘online’ identity with a ‘real world’ named individual.

The data subjects are identifiable if they can be directly or indirectly identified, especially by reference to an identifier such as a name, an identification number, location data, an online identifier or one of several special characteristics

By definition commenting reddit users are covered, even if they haven’t posted anything otherwise identifying – but most have either way.

If a user is commenting they have an online identifier and are thus covered. If a user has ever referenced their relationship status, location or any physical descriptor they are covered. The GDPR – it applies.