What does this sentence mean 我是男猪脚?
This is internet slang: 猪脚 refers to 主角 (they have similar pronunciation), i.e. protagonist / leading role [character]. The original meaning of 猪脚 is pig feet; as @NS.X. commented, as internet slang it's usually used for playfulness, sarcasm or self-mockery.

我是男猪脚 means I am the leading man (main actor).

Related terms: 男猪 (男主角), 女猪 (女主角).