Well, this is my last resort. Whenever I've seen this image used as a reaction image, I've asked for sauce and no replies. Checked SauceNao and no relevant answers so....sauce?
I must really be a hentai fiend because I thought "I think I remember that panel". She is walking in on her brother jacking off to porn, hence the sound effects in the panel.
http://www.tsumino.com/Book/Info/17883/1/sm-melts-in-your-mouth-and-between-your-legs-sm
Adding a couple more pages as a preview.
>>4291430
>tsumino
Not even once.
>>4291430
Finally, thanks man.
>>4291435
I know he's into it judging by the title, but shouldn't there be a bigger reaction for getting your dick stomped on? Never had it happen to me, but I imagine it hurts more than that.