The crafty chad is attempting to put your penis into a girls arse hole repeatedly after she has warned you she doesn't want anal. The male will attempt this many times over untill the girl is enraged and will no longer engage with him in sexual conduct. In doing this you also cock block your friend who also trying to get laid for the first time with the girls friend.
An expression commenly used for people who do things secretly or are very skilled at something. It really has nothing to do with hippos, just the fact that hippos are very craft and trixy.
Viviana walks up behind Linnea while she's talking toVeronika and Kaylee
Viviana: Hello Liddea!
Linnea: Ahhhhh!! You scared me vivi, you crafty hippo!