Lithuanian here.

What mostly grinds my gears is Lithuanians taking an English word and adding a Lithuanian ending, and often even a wrong one:

breakupinosi instead of išsiskyrė, faitinosi instead of mušėsi , etc.

Some other gripes include optimaliausias i.e. most optimal. Optimal is already the best, what is the point of saying bestest?

Adding pointless phrases like ta prasme i.e. in that meaning is also common but seen as a major style error.