Daylight Savings Time.

Europe switches to DST this month and specs are broken because of Ruby's DateTime which isn't DST-aware so it generates invalid dates and can't do date math properly. Losing a couple days to refactoring horrendous code that uses *nested* Timecop.freeze, mixtures of Time, Date, and DateTime, math and parsing revolving around the end of the month.

Death to DateTime and death to DST.