The phrase "huge slap" means a big or significant blow or hit, either physically or metaphorically. It can refer to a powerful hit or a sudden and surprising event that has a major impact. Full definition
Just one huge slap in the face, especially after his failings of not getting a centre back last year. (justarsenal.com)
The TaxPayers» Alliance called the party a «huge slap in the face to all those who have struggled under the Bank of England's policies». (goldsilverbitcoin.com)
In New Member's Class, because they RRRRRREEEEAAAALLLLYYY want you to join their church, they don't tell you membership is conditional upon the fact that you NEVER commit a sin they think is, like, a HUGE slap in the face to their public image. (nakedpastor.com)