About
I have an Army/we have an X is an expression of the power of one person or object as compared to an army, whether or not it is more powerful or so non threatening it makes no sense.

Origin
The first use of this phase was used in the 2012 film the Avengers when the villain Loki is arguing with Tony Stark before the start of the final battle. As Tony explains the Avengers to Loki, Loki gets fed up and aggressively states "I Have An Army" before Tony replies pretty smug like with "We have a Hulk."

https://www.youtube.com/watch?v=MMpCCo8Evnc

Spread
After the popularity of the Avengers, this became a favorite quote among the internet, especially when discussing who is more powerful in the context of an argument. It has also been comparable with many other famous figures who claimed to have something in their possession deemed either powerful, or something very non threatening as to seem ironic. The most prominent has been with Jack Sparrow's response to Davey Jones in the second pirates of the Caribbean movie.

Notable Examples

https://www.youtube.com/watch?v=XDEUZdtcfrw

https://www.youtube.com/watch?v=B1DqdkqQOA0