The phrase "sucking up" often has negative connotations, implying insincere flattery or an attempt to gain favor through excessive praise. Some synonyms for this phrase include brown-nosing, apple-polishing, groveling, toadying, fawning, flattering, and kowtowing. These words all convey a similar idea of trying to win someone's approval by being overly obsequious or flattering. In a professional context, employees may engage in this behavior to get ahead or gain favor with their boss, but it can also be viewed as manipulative or disingenuous. Ultimately, it is important to strike a balance between being friendly and professional without resorting to excessive flattery or insincere behavior.