。
Your thread title's wrong, dude.
Literal
Thread-title wrong-[-てる] [emph-ぞ].
スレタイ is an abbreviation of スレッドタイトル 'thread title,' standard internet-forum slang. 間違ってる is the casual い-dropped contraction of 間違っている. The masculine assertive ぞ closes with a friendly-but-pointed 'hey, just so you know.' A minimal utterance saturated with net-slang and casual morphology.