Yolkamebob - an important object or technical component of something that you don't understand -
"Sorry we're late Betty, but the car wouldn't start until Paddy fiddled around with the yolkamebob" Thingamijig - an object you've temporarily forgotten the name of - "Paddy, are you sitting on that thingamijig to change the channel?"
Whatchamacallit - same as a thingamijig -
"I'm meeting Nuala for a pizza tonight so I'll miss the Late Late, but sure I have it set to record on the whatchamacallit!" "a few onions short of a stew" - not the full shilling - "Would ya look at the outfit on that one Grettie?". "Ach, don't mind her Annie. She's a few onions short of a stew!"
Wojus - of poor quality; terrible - "Dorothy was telling me herself and Dick tried that new Chinese restaurant the other night. God she said it was wojus altogether!"