Several "Americanisms" piss me off!
"Reaching out" when talking/contacting someone.
"I'll get a...." as opposed to "please can I have"
Plus spelling.
Z used in place of S, example colonize and colonise
S used in place of C, example offense and offence
Both examples used in this thread by, I assume, people educated in the UK..
Funnily enough though, the omission of the letter U in words like colour doesn't bother me. Hey oh.