Talk a good game
Definition 1 of 1
Pro Tip 1/3Confidence vs. Capability
The phrase often implies a disconnect between what someone says they can do and what they actually achieve. 
Despite claiming to be a top-tier programmer, he seemed to only talk a good game.
Pro Tip 2/3Skepticism Cue
Use this phrase to express doubt about someone's abilities when they haven't shown proof. 
She always talks a good game about her leadership skills, yet her team is in disarray.
Pro Tip 3/3Informal Idiom
Best used in casual conversations or informal writing, not in formal contexts. 
At the party, he talked a good game about his investment strategies.