In the video 'Ruby ate my DSL!' presented at RubyConf 2019, Daniel Azuma discusses the challenges and intricacies of designing Domain-Specific Languages (DSLs) in Ruby. He emphasizes that while DSLs can simplify coding by introducing expressive and concise syntax, they uniquely interact with Ruby's underlying mechanisms, which can lead to unexpected issues.

Key points covered include:

- Introduction to DSLs: Azuma defines DSLs as methods that don’t require a receiver object for invocation. He highlights their usefulness in creating commands that resemble native Ruby syntax.

- Common Pitfalls with DSLs: He illustrates how conflicts can arise when DSLs utilize method names that overlap with Ruby standard library methods, citing a personal experience with a Sinatra application that led to a debugging challenge due to a method name conflict.

- Using Metaprogramming in Ruby: Azuma discusses how DSLs leverage Ruby's metaprogramming capabilities, e.g., the Rails framework uses instance_eval to dynamically change the context of a block. This allows DSLs to extend their functionality while still being rooted in Ruby.

- Control Over User Input: The speaker warns that DSL users often inject standard Ruby code into the DSL. Thus, designers must anticipate how end-users might misuse their DSL and incorporate defenses to prevent unexpected behaviors.

- Creating a Sample DSL: To solidify his points, Azuma teases the creation of an illustrative DSL called 'nano_spec,' aimed at showcasing Ruby DSL designs and their challenges.

The presentation underlines the importance of intentional design in DSLs to ensure both usability and safety when integrating Ruby features.