Jon says:
One of these mutant fighters was sporting some Chinese tat, that, upon further inspection, was actually Japanese. I think it's trying to say, "I'll win in spite of yesterday?" or something like that.
Plus, making "I" two characters wide on the top makes it confusing at first glance to figure out if it should be read top-down or left-to-right. Anyway, not sure your final verdict on this but it's totally suspect.
HS senior resident pro-bono Japanese consultant Alan Siegrist concludes that:
The order of characters is strange, and I guess someone has left out a few words or characters. The grammar is also wrong because they are using the future tense for something that happened in the past.
This is very weird.
Anyway, I guess the intended order is: 我は昨日のに勝つ.
This would mean roughly something like "I will win yesterday's ___."
I guess the word in the blank is supposed to be "match" or something, since these guys are some sort of MMA fighter guys.
Maybe he didn't have enough money to let the tattooist finish the tattoo or maybe he weenied out at the last minute. Maybe he couldn't stand the pain.