Flags in a database rows, best practices

Generally speaking, I avoid bitmask fields. They’re difficult to read in the future and they require a much more in-depth knowledge of the data to understanding.

The relational solution has been proposed previously. Given the example you outlined, I would create something like this (in SQL Server):

CREATE TABLE Users (
  UserId INT IDENTITY(1, 1) PRIMARY KEY,
  FirstName VARCHAR(50),
  LastName VARCHAR(50),
  EmailAddress VARCHAR(255)
);

CREATE TABLE Badges (
  BadgeId INT IDENTITY(1, 1) PRIMARY KEY,
  [Name] VARCHAR(50),
  [Description] VARCHAR(255)
);

CREATE TABLE UserBadges (
  UserId INT REFERENCES Users(UserId),
  BadgeId INT REFERENCES Badges(BadgeId)
);