According to her:
From the 1st Flash Annual, Wally in boxers! And it's even meaningful shirtlessness - this was back when Wally was just taking over for Barry and feeling pretty angsty about it, and the villain said he wasn't fit to wear Barry's costume and zapped it away. (I find it unlikely that Wally would wear boxers under such a tight costume, but I'll take what I can get.) And then Hal came and was a big asshole, because that's how Hal rolls. It was a bad day for poor Wally.