I saw this cartoon years ago in an issue of 'Easy Rider' magazine
Picture two bikers puttin' down the road on their Harleys. One has a little tiny head. The other says, "Bro, you really gotta get your ol' lady to lay off the Preparation H."

Another joke about a "diminutive dome."

A guy's sitting at a bar. Another dude takes the stool next to him. This dude has this really small head, which the first guy notices right off. He keeps checking this dude out, but doesn't want to say anything, for fear of offending him. Finally, his curiosity gets the better of him. He says, "Yo, dude, I gotta ask, why is your head so friggin' small?" The dude says, "Well, it's like this. I found this old rusty lamp half burried in the sand. I dug it out, rubbed it off, and out pops this drop-dead gorgeous female genie. She gave me three wishes in return for freeing her. So, first I wished for a fully loaded Bently. I always wanted one of them. Poof - there I am sittin' in the driver's seat of a brand-new top-of-the-line Bently. Then I wished for $100 million. Poof - I'm surrounded by rows and rows of neatly stacked bills. Then I got to thinkin', what more could I possibly want or need that I couldn't buy with all this money. Now, this genie was fine, I'm tellin' ya. Stone fox. Really turned me on just lookin' at her. So, while I was tryin' to think of what else to wish for, I said, 'How 'bout a little head?' Poof ... ... ..."