"Corny" jokes are jokes that are only slightly amusing. They are often a play on words or have an obvious conclusion that makes you roll your eyes.

Humor is so hard to translate! I laughed because "pikachu" sounds like "peek at you" -- it's a pun. Lady Gaga sang a very popular song called "Poker Face," so "poke her face" is also a pun. "Sticky" is another pun. If you imagine something that is 茶色 and also 粘い, you probably are not going to imagine 枝. Now as to why we call them "corny" or "lame", this is because we laugh, but we also groan a little. Like that was really stupid, but it was still funny. 日本語で「それは愚かだったが、それは面白かった。」といいますか。

Thanks a lot everyone. After getting the meanings, I indeed rolled my eyes and ｓill laughed. 日本語で言えば「くだらないけど可笑しかった」と言ったところでしょうか。