C'est pas le pogo le plus dégelé de la boite.

It kind of translate to: He/she is not the most unfrozen pogo in the box.

It implies that someone is not the smartest person around, actually the opposite.

In Dutch: 'graftak' is a beautiful way to indicate an annoying/terrible person. Literally: 'grave-branch', which sounds nowhere near as satisfying.

It's archaic but I love "raclure de bidet". Comparing someone to the stuff you would scrape off of a bidet where all sorts of people have washed their taint. Short and loaded with contempt.

"Gibier de potence" is great too. Means "game for the gallow", with the term "game" using in the hunting sense. Basically someone you think should be executed.

Also "chien sale", dirty/unclean dog, which for a reason is a stand-in for "asshole".

"No me friegues, cara de tostada" don't fuck with me, tostada face. Much worse if the target is a spanish speaker.

It's not an insult but a way to show frustration without hurling insults.
So here in Russian like
ЁКЛМНЭ
ЁПРСТ
Ёшкин кот
Блин (pancake) to not use Блядь (whore)
Мать твою за ногу
Пиздец
Ппц
hmm that's all that comes to mind unless going into really insulting words.
In romanian I know only "Du-te in pula" "Du-te in pula mea" which is Get Fucked, fuck off.

Australia:

"Fuck off ya fuckin gronk!"

Or Ya fuckin mutt cunt!!"

Me cago en la leche de tu puta madre

That's one I picked up in Málaga. Fun place haha

"live fast and get fucked or whatever"

Not really an insult but it kinda sounds like one.