Someone who looks so lovable, adorable, etc
It would be used in the context like
" 아우우우우 >_< 이 사랑둥이!! "
Call your friends this, then he/she will throw up,
Call your lover this, then he/she will blush.
People around you will get some goose bump of hatred.. I assume
Cf. 귀염둥이 = someone with lots of cuteness