Based on what I played of the game, I feel that the awful meme jokes in the challenge titles are self-aware. When they put them in the game they weren't thinking "let's put these hilarious internet jokes in here guys", they were thinking "let's put these super played-out internet jokes in the most blatant way possible, so when people see it they are just forced to groan at how bad they are", that’s why those challenges are funny to me.
That said as I was playing the game today I shot a badass in the head and as he died he yelled "AAHHHH Pluto isn’t a planet !!!", and I just completed a side-quest based on the movie Top Gun, so I believe the humor in Borderlands 2 to be great.