Chad Johnson -- Wears 'F**king' Shirt .. TO KIDS TOY STORE!!!

Chad Johnson had a big, bold message printed on his t-shirt for all the little boys and girls at Toys R' Us to see on Christmas Eve ... "CARPE THAT F**KING DIEM" kids!

The former NFL star hit up the toy store in Pembroke Pines, FL to pick up some last minute gifts on Tuesday ... and actually decided to wear a shirt with the word "f**king" written in huge letters on the front.

Of course, the rest of the phrase was written in Latin ... so kids probably wouldn't get the "seize the day" message ... but "f**king" was written in plain English for everyone to enjoy.

We reached out to Chad for comment -- who told us, "I should've went in with no shirt."