凑个热闹 Wuddaya / toleja

Whatchamacallit
It is derived from the phrase "what-you-may-call-it" 

what you -> 口语读成 whatcha
may ->　口语读成（弱化）/muh/
call it -> 口语连读成　callit
--->  whatchamacallit

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Etymology of the English word thingamajigger

the English word thingamajig

derived from the Obsolete English word jig

derived from the Obsolete English word thingum

http://www.myetymology.com/english/thingamajig.html:

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What the hellja do that for?
Wuddaya want the light for?
Listen, I toleja about that ... blah blah ...