Looking on the internet deeply has found these results:

I was bad yesterday is the most popular phrase on the web.

I were bad yesterday. 10 results on the web	I was bad yesterday 187 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	I was bad yesterday but staying active, cleaning, gardening, etc.. helped a lot. I didnt get much sleep last night, but I woke up feeling so good�... Feb 6, 2014 ... (That really means that your fingers are not working correctly.) Correct: I was bad yesterday and I'm sorry. (Note that was is a linking verb.)�... Apr 25, 2012 ... I'm glad Eli is okay :) I tend to eat my worries, too, but as long as it doesn't put you in that "oh well, I was bad yesterday so I'll keep going all�... Jun 9, 2013 ... "Everyone was telling me I was bad yesterday and I didn't feel like I was bad, but I really got it going, got with my receivers and really did a good�...

I were bad yesterday.

10 results on the web

I was bad yesterday

187 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

I was bad yesterday but staying active, cleaning, gardening, etc.. helped a lot. I didnt get much sleep last night, but I woke up feeling so good�...
Feb 6, 2014 ... (That really means that your fingers are not working correctly.) Correct: I was bad yesterday and I'm sorry. (Note that was is a linking verb.)�...
Apr 25, 2012 ... I'm glad Eli is okay :) I tend to eat my worries, too, but as long as it doesn't put you in that "oh well, I was bad yesterday so I'll keep going all�...
Jun 9, 2013 ... "Everyone was telling me I was bad yesterday and I didn't feel like I was bad, but I really got it going, got with my receivers and really did a good�...