1. slang Arrogant and snobbish. I was already bored, but now that we have a snot-nosed tour guide, I'm leaving. Did you hear how judgmental he was about our choice of wine? What a snot-nosed jerk.
2. slang Young and inexperienced. I've been in this job 20 years, and now some snot-nosed kid right out of college is going to tell me what to do? No way!

snotnose(d) kid

and snotnose
n. a young child; a relatively young person. (Rude and derogatory.) Some little snotnose swiped my wallet.
See also: kid, snotnosed