"Y tho" is a term used regularly nowadays. Stemming off of the phrase "why, though" it has been recently used to show confusion in a trolling type of manner. If, say, someone does/says something unintelligent, it is appropriate to reply with "y tho". For people not to confuse "y tho" with "why, though", squint your eyes while protruding your neck and calmly, in a small voice say "y tho?".
(Also there is a meme associating with this phrase.)
Person 1: Honestly, y'all are just vapid, y'all should leave.
Person 2: y tho?