Sorry, you learned the kun'yomi reading with 広. So, think of it this way when you need to remember this word's meaning: You're advertising something. It's a big advertisement to advertise how terrible a person こういち is. Come up with some terrible things he's done so that you can imagine this crazy Koichi advertisement you made and ran on national TV.
In a book I borrowed from the library, there was a grocery store advertisement stuck between the pages.
I have to go back home because I forgot the ad with the coupon.
Viet informed Koichi that Aya created the strangest picture ever for Tofugu’s advertisement.