OK. Humor me. Time for some Jr. high school level levity... Looks like I found a great Vietnamese restaurant in Yotsuya 3 Chome. I saw it because of the sign and thought, "What the Phuoc!?"
Looks delicious! Their average rating was 3.3 out of 5 so that's really good for a reasonably priced restaurant in Tokyo.
Heck, since I make fun of their sign, I have to at least give them a plug! Here's a map and a website. My friend told me that he loves this place and eats there very often. The lunch sets during the week are a super good deal at ¥550! (about $6 USD):