知ったかぶりをするのはおかしいです。
It's strange/odd/weird that you pretend to know about "X"
when/which you actually don't know about.
上記のほかにtalk about やspeak aboutを使っても、
ここでは同じ意味になります。
It's strange/odd/ weird that you talk about "X"
when/which you actually don't know about.
It's starnge/odd/weird that you speak about "X"
when/which you acutually don't know about.
pretend to know で知ったかぶりをする
weird も おかしいの意味です。