This little EV maker still has a lot to prove.Rivian (RIVN 3.43%) was one of the hottest IPOs of 2021. The electric vehicle maker went public at $78 on Nov. 10 and closed at its record high of$172.01 six days later. It initially impressed the bulls because it had already started mass-producing its first vehicles, and it was backed by Amazon (AMZN 0.79%) and Ford (F +1.45%). The buying frenzy in hypergrowth and meme stocks in late 2021 further inflated its valuations and amplified its gains.At its peak, Riv ...