YES. I feel like I'm one of the few that loves this movie- Paul Rudd has really earned my respect over the years. I'll add Role Models to the list.
I have always loved Dodgeball. My list would also have to include Accepted and Kicking & Screaming with Will Ferrell.
GREAT choice. My 2 favs (probably not underated but love em anyways) NSFW <iframe width="560" height="349" src="http://www.youtube.com/embed/l0_S_EdZ_I8" frameborder="0" allowfullscreen></iframe> and <iframe width="425" height="349" src="http://www.youtube.com/embed/BfeZXWXmI_0" frameborder="0" allowfullscreen></iframe>
I'm gonna get you sucka. So underrated. <iframe width="425" height="349" src="http://www.youtube.com/embed/KNQRqAoT-2c" frameborder="0" allowfullscreen></iframe>
I'm Gonne Git you Sucka and sadly a movie almost no one including their mothers haven't seen, Johnny Dangerously. That movie seriously had me laughing non-stop.
<iframe width="425" height="349" src="http://www.youtube.com/embed/XAl-ZyI8R5Y" frameborder="0" allowfullscreen></iframe>
Dumb and Dumber wasn't underrated, it was made in the 90s but it still gets a mention every now and then on internet forums and in real life. Very quotable movie. An underrated comedy is Pineapple Express imho.
The Party starring Peter Sellers is I believe the only Blake Edwards non-Pink Panther movie that was made. I think it's better than Dr. Strangelove. Absolute gem of a movie to get a glimpse of what the late 60's were like. And I agree with the other posters here who said Mallrats and The Gods Must Be Crazy. Mallrats because it's probably the least talked about Kevin Smith movie but still has great one-liners like "Brenda? Dick". And The Gods Must Be Crazy More recently, some better and severely underrated comedies would be Josie and the Pussycats and Bend It Like Beckham. The scriptwriters for Josie and the Pussycats did a masterful job, supporting actors like Alan Cumming, Missy Pyle, and Rosario Dawson put on really mature performances holding it all together, and Parker Posey has in my opinion one of the best characters of any movie I've ever seen. And Bend It Like Beckham...well it started the careers of Keira Knightley, that British guy from the Tudors, and that Indian girl from ER.