Not necessarily happy, but based off, or similar to ~imhappyplz (https://www.deviantart.com/imhappyplz) I know that I'm missing many popular ones, so please comment with the ones you have!
:iconImhappyplz:+:iconUrhappyplz: - iconImhappyplz + iconUrhappyplz
:iconImhighplz:+:iconUrhighplz: - iconImhighplz + iconUrhighplz
:iconiloveyouplz:+:iconiloveyoutooplz: - iconiloveyouplz + iconiloveyoutooplz
:iconimseriousplz:+:iconurseriousplz: - iconimseriousplz + iconurseriousplz
:iconnewlightplz:+:iconhappylightplz: - iconnewlightplz + iconhappylightplz
:iconimnothappyplz:+:iconurnothappyplz: - iconimnothappypplz + iconurnothappyplz:
:iconcrosseyedplz:+:iconwalleyedplz: - iconcr