Manga with obsessive female after unwilling male, but she can't be stupid, like she has to at least know what she's doing. Doesn't have to be main character, but would appreciate it. Also can be anime. Even better if it's both.

Chips?! In a tube?! That's just crazy!

do you go for a smut?
try Junjo Shodo

Girls Saurus is about a bunch of girls after a very unwilling guy, their intelligence levels vary. Also one of the funniest mangas I have ever read.
Hayate no Gotoku!
Mahou Sensei Negima! some of the girls work, if you don't mind that the reason he is unwilling is age
Mirai Nikki The girl is very smart, but the willingness of the boy varies
Übel Blatt

Hope it didn't have to be shoujo 😁

Gakuen Ouji - whole bunch of sexcrazed schoolgirls after a very unwiling transfer student.

if you don't mind shoujo
baby love
tokimeki tonight
but I don't think the females are obsess with the main male character. Well... you can say teenage obsess level but not a maniac 🤣

by the way, second gakuen ouji

Help! I'm looking for... manga with dangerous guys [url]http://www.mangaupdates.com/showtopic.php?tid=39874&page=1#post594033[/url]

Perhaps Uwasa no Midori-kun (no anime) and Midori no Hibi (anime).

You could say that Koukou Debut starts out that way, but that part of it is over relatively early.

Aya from Tenjo Tenge (anime) definitely fits.

Oh, and I third Gakuen Ouji.

If you've ever thought or said "Nice Guys finish last" and really meant it, then you should probably read this LJ post by DivaLion. It's incredibly insightful whether you're male or female.

From a bumper sticker I like:
"If you're gonna ride my ass, at least pull my hair."

Nodame Cantabile he's unwilling in the beginning.
Rosario to Vampire
Kodomo no Jikan Rin is pretty obsessive
Mousou Shoujo Otakukei not Rumi but the other fujoshi whose name I cannot remember. sort of.

I know in Sister Trap there is that element but it's really adult

That's all I have for now.

"I've seen a look in dogs' eyes, a quickly vanishing look of amazed contempt, and I am convinced that basically dogs think humans are nuts." -John Steinbeck