1. Guerilla usability refers to unconventional and pragmatic methods for improving usability in government organizations through grassroots efforts. 2. Government organizations need guerilla usability techniques due to challenges like getting consensus among stakeholders, time constraints, and risk aversion that can stall projects. 3. Overcoming barriers involves gaining support from colleagues, leveraging existing processes, and using tactics like starting projects without official approval or under different names to bypass bureaucracy.