His girlfriend's inner thoughts leak out constantly, and just being with her is embarrassing.

My childhood friend is, for some reason, unable to keep secrets—or rather, his inner thoughts completely leak out—basically, he's an honest guy who tells everything. The other day, he suddenly blurted out, "Oh, that girl's skirt from the previous high school is flipping up," and because of that, I was mistaken for doing something and got beaten with a wooden club. Every day I wish he would just suppress his inner voice a little bit.