"Even though the National Guard and Army Reserve see combat today, it rankles me that people assume it was some kind of waltz in the park back then"

In this quote, Larry David is revealing disappointment with the common misconception that serving in the National Guard and Army Reserve throughout previous disputes was an easy and carefree experience. He acknowledges that these branches of the armed force are still involved in combat today, but he is bothered by the fact that individuals presume it was a simple and satisfying task in the past. David's usage of the word "rankles" suggests that this misunderstanding greatly troubles him and perhaps even angers him. He wants people to understand and value the sacrifices and challenges that were dealt with by those who served in the National Guard and Army Reserve in the past.