I ran across this word while reading about a gathering for 성소수자 (sexual minorities) to deal with issues in the workplace.

The first question includes the word 일코 which is defined here as 일반코스프레. This word is usually used within straight communities to hide something that might be considered odd by the general public. For example,

'나 '일코'해서 아무도 내가 Kara 좋아하는 거 몰라' could be interpreted as something like 'I am good at hiding the fact that I like Kara so nobody knows about my fandom'.

The word has also been used by the gay community by playing off the fact that in gay speak, 일반 can refer to a straight person (opposite of 이반). So in the above poster,

이럴 때 내가 일코 (일반코스프레) 정말 잘한다고 느끼나? would be 'Do I feel as if I am good at playing straight at those times (at work)?'

I saw another usage on a queer bulletin board where a young woman who identified as heterosexual was confused about her sexual interest in her 언니. One commenter said:

그냥일코하고 사시는건 어떨지...? How about just living as a straight person?

Not the best advice, but a good use of the word.