Absurd, Ridiculous, Silly
い adjective
Remember how you learned that 馬鹿 means "idiot?" Well put two idiots together and everything they say and do is absolutely absurd. Remember how ridiculous that "Dumb and Dumber" movie was? Yeah. Like that.
ばかばかしい
You already learned 馬鹿, so as long as you can remember it twice in a row, you should be able to read this too!
馬鹿馬鹿しいこと言わないでよ。
Don’t say stupid things.