What are those mean??

1.Stick it back in all our faces
表面句子是「把it貼回在我們大家的面前]
喻意可能是(因為要知it是甚麼才能肯定)「把難題(it)扔回給我們去處理」。
2.Peppering me with questions
peppering是借喻作「撒/灑」(pepper spray是胡椒噴霧，向攻擊的人作為防衛)這句表面意思是「問我很多問題」喻意是「你用很多問題來為難我啦」的負面意思。3.Set fire to the sidewalk
set fire正意是「縱火」
喻意是「激起熱情」
表面的意思是「在行人路上放火」，
沒有前後文而你是問idiom的話：可能是「令原來沒有興趣的人(或旁觀者)也熱情/狂熱起來」

Stick it back in all our faces - retaliate on us

Peppering me with questions = asking me a lot of questions. ("pepper" is used figuratively)

Set fire to the sidewalk = deliberately caused the sidewalk to burn

set fire=to ignite someone or something; to put someone or something to flames
peppering with=to shower someone or something with something, such as stones, bullets, etc. e.g.The angry crowd peppered the police with stones. The sheriff's posse peppered the bandit's hideout with bullets.
Stick it to=to give someone a problem; to confront someone
so stick it back maybe the question is back to us

第二句：

即是「像撒胡椒粉的不斷問問題～」

http://oxforddictionaries.com/us/definition/american_english/pepper