in what ways does Washington Irving poke fun at the idea of the new american hero?

Here is something that should help. Pay attention to his anti-heroic traits like "laziness", his relationship with his wife....Although Rip is a loner, he is not a roaming loaner in the classical sense; he is actually rather bumbling and comical.

"Rip Van Winkle," a classic American Romantic tale, presents a hero that embodies several characteristics important to the ideal romantic hero.

Rip is isolated and alienated by his long sleep, and has trouble accessing the new, strange world of the future. Themes of the supernatural and fantasy are very prevalent in Romantic literature, as is the theme of nature. In RVW, these elements are what help to isolate Rip from society, thus creating the sort of iconic loner character so often found in Romantic fiction (see Melville's "Bartleby the Scrivener" for another example).

Romantic heroes tend to be archetypal rather than well-rounded, realistic characters, and often meant to embody ideas rather than represent humanity (something that changed once Realism came about). In this case, Rip fulfills the classical role of the Romantic prophetic awakener. In this particular instance, the ideal is explored through metaphor (he "wakes up" in the story). Rip also has many antiheroic qualities (the Byronic hero comes to mind), such as laziness -- this tempering helps us separate him from the neoclassical idea of the perfect hero. A romantic hero often has flaws.

Rip's heavy involvement with nature -- it works as a setting and more in the piece -- also helps identify him as a Romantic hero. Romantic heroes are almost always seen as having direct involvement with nature, which is sometimes presented as wild, untamed, and dangerous.