Nice guitars ruined by one feature...

SPECTRUM001

Narrow Tall or Jumbo fretsize is the one for me. 

I saw, I tried, I failed....

Tannin

sweepy said:

and Allen bolts made of cheese 

This 100 times. And not just guitars.

Cols

Washburn N4 - no tone control, complemented by an ear-splittingly bright bridge pickup.

Philly_Q

Wasn't there another thread on exactly the same topic recently (much more recently than February 2020)?

PLOP

Strat, Jazzmaster: front mounted output jack. 
Tele: No contours on the front or back. 

LP: Pickguard. 

Others: Quilted or flamed tops. 

StuartMac290

The headstock on a PRS. And the body.

RichAC

My HB kit guitar has the serious flaw that it was built and painted by a ham-fisted moron. 

Voxman

zepp76 said:

Any Les Paul with no scratch plate on.

FTFY

Voxman

For me I don't like open pick ups. I can just about tolerate open pickups on my PRS Cu24 and Patrick Eggle Berlin Pro but for a Les Paul or SG it just has to be covered pickups.

I also want scratch plates and poker chips on a Les Paul.  

Other turn offs for me are:

locking nuts
Floyd Rose trem bridges
Overly ornate fingerboards
Fingerboards with no fret markers
Pointy guitars
Robot funers
An excessive number of knobs and switches
Baseball bat necks

Littlejonny

The floor in the design of the strat - you have to take the strings off to get at the electronics. Having an access panel on the back is so much better.

And all semi-hollows - no access panel for the electronics at all. Come on, just a Les Paul style panel on the back is all that’s needed!