there are so many good responses here.
the automobile horn - it has a purpose, but it has been corrupted like like slain corrupts language (not looking to start a slain war). people use it to say "hi" to that guy over there surrounded by twenty other guys. people use it impress on the guy in front of them that even though there are cars coming from the other direction, the guy isn't turning left (right for the UK) fast enough. instead of a honk to notify, people will lean on the horn, bang on the horn repeatedly, because instead of saying "hey i'm here, watch what you are doing" people want to say "WTF WTF YOU F'N IDIOT! LET ME STAB YOU WITH THIS CAR HORN OVER AND OVER AND OVER AGAIN!" and of course the single best thing a car horn is good for is annunciating exactly who it is address at. i've been in a car where the driver was using the horn as a percussion instrument. we were in a rural area surrounded by crops, but it was still painful.
car horns are #1
cellphone - as a phone, they barely work as a communication device. true, they transmit noise, and it is sort of intelligible.
i too dislike technology put in place to make life easier, but not the maintenance side to keep it work.
i guess cellphones are the only true technological inventions in my list. the others are just more examples of people misusing technology.
no, i'm not doing an e.e. cumming things. the thought of car horns made want to be the opposite of all caps.