Hehehe...this is from a doujinshi called Mince Special (which I think I mentioned elsewhere around here, since somebody has a scan in his/her sig). That particular scan comes from a larger gag story. I'm too lazy to dig out my copy, but I believe it was set much earlier in the series and the setup goes like this if I'm remembering it right:
Inuyasha and Kagome are having yet another fight, and Miroku bets Sango that Kagome will stay home for three days this time (being so mad at Inuyasha and all). Inuyasha sulks. Then, he eventually decides he should take matters into his own hands. He goes to her time and since she's apparently not at home, he slinks into her room and starts looking around for the Shikon shards. These two pages explain what follows (and yes, they are a wee bit ecchi in implication ^_~):
Inuyasha searches through the drawers.
IY (thoughts): But those shikon shards are coming with me!
IY (thoughts): Hmmm, this drawer smells nice.
He finds a pair of panties, and is confused.
IY: ...
He looks at them closer.
IY: What the heck are these?
He pulls them onto his head, like a hat. His ears stick out through the leg holes.
IY: What a weird hat!
IY (tiny text): It even has ear holes.
He thinks about this some more.
IY: Although there's sure a lot of 'em, if they're supposed to be hats...
He involves his nose by wadding up a pair (yes, I assume they're clean!) and sniffing.
IY: Kagome's scent...smells good... (This is literally "Kagome's good scent" -- you can read it in a perverse manner if you so choose ^_~)
And then, in a very hilarious scene, Kagome walks in to find Inuyasha messing around with her underwear drawer.
Kagome: !!!!
Next scene: Back in the Sengoku Jidai, and Inuyasha looks like he had the crap beaten out of him. In the background, Miroku is collecting his money. This implies that he has won the bet, and Kagome is staying her time for a Very Long Time

Miroku: Ahahaha, that's too bad Sango...better luck next time!
Shippou stares at Inuyasha.
Shippou: You must be a complete moron.
Inuyasha sulks.