I've forever been having problems open up the super smooth Bluetooth headphone cases.  It got to the point where I'd just stop using them.  Then I printed out some finger grips.  Problem solved, use them every day and I've never had an issue with them snagging or accidentally opening the case.

I printed out some flat, tapered, ridges.  Warmed them with a heat gun and them form fitted them onto the oval face of the case.  Within seconds they kept their shape and then I just dropped on a bit of epoxy.  Done!

The first version of these didn't have the tapered sides so I quickly cut them off with a utility knife and then redesigned the print to include the taper.

Infill doesn't come into play as the print is so small as to not have any empty spaces.  I did however print at .15 so it was as smooth as possible. 

I used a generic PLA for this and print time was just a few minutes.  There's a single download so I doubled it up in my slicer.

When heat forming each piece onto the case don't forget which is top and which is bottom, just in case the curve is different. Also remember orientation, drop a small dot of ink on one side so you always know which way it was fitted onto the case.

I used a 5 minute plastic epoxy to glue the grips onto the case.  less is better and clean out any squeeze out if you have any.  I used some scotch tape to keep them in place and left them, grip side up, on my bench until cured.

I get the whole “smooth egg” concept for these headphone cases but this will be my Go-To mod on every one I have or will have.  I've even printed off some for friends who had the same problem I did.

Here's a hint, if you want something less obtrusive on your case just drop the height a bit.

Good luck and good printing!

Like my design, how about a cup of coffee?