Plants I don't get

B3

I can sort of understand the appeal of camelias, but after a bit of rain, they look like Miss Havisham's wedding bouquet.

Forsythia are too leery for eyes used to winter ditto leery tulips

Ceanothus blossom doesn't match the dark leaves.

Variegated leaves with blossom is too much of a good thing. It reminds me of that ex soap star who covered herself, her baby and the pushchair in burberry tartan - less is more.

Sweet peas  - after a few weeks, they're dead at the bottom. This doesn't make up for the smell.

Ground cover plants cover the ground because they're thugs

Double flowers are an abomination.

Petunias are sticky
I
Philadelphus is blackfly heaven 

Well, that's got that off my chest😊

pansyface

“Black” flowers and “black” leaves.😞

Purplerain

I don't get Cherry Trees.  They look awful for most of the year, but begin life in a benign fashion like little umbrellas, then they blow their annoying blossom all over the road within a week. I would ban them. I think Magnolias are just as bad but that is just my point of view 😀.

Paul B3

Those hideous hybrid Gladioli stems often for sale outside petrol-stations etc .....stick to the proper species!!!

So-called 'Azaleas' sold by 'florists' ; flower once and often collapse into a mildewed mess.

Forced Hyacinthus bulbs grown for Winter ; look much better growing naturally outside .

Agree wholeheartedly with B3 ; double flowers are awful , and virtually useless for pollinators .

Bedding plants !!!......Do people actually still grow these??

Mr. Vine Eye

Pom-pom dahlias

nutcutlet

lilies. spiraeas, all of them. Double flowers generally. anything with yellow leaves and pink flowers. 

purplerallim

Anything pink, lily of any type ( the smell) lupins (earwig hotels), and most of all ivy.

Paul B3

I forgot to mention the infamous 'Kilmarnock Willow' !

Busy-Lizzie

OH dear, I grow and like a lot of the above.
I like the confetti of Cherry trees, I love pink, lilies and lupins but I hate ivy, the wild sort. I like spireas and everything on @B3's list.
I agree with @pansyface, not keen on black flowers. Not keen on green flowers either, what's the point when the leaves are green?

Paul B3

There is one garden we see frequently en-route to Boston (Lincolnshire) during the Summer months ; bedding Begonias planted in a perfect line equidistantly @ 8" apart .

Now there's natural planting if I ever saw it !

Purplerain

The Kilmarnock Willow is a real let down ☹️.