Teachy is a slang term that refers to someone who is overly instructive or pedantic. Fortunately, there are plenty of synonyms that can be used in its place. For example, instead of saying someone is "teachy," you could call them didactic, academic, or preachy. Another option could be to describe someone as being lecturing, educational, or informative. It all depends on the level and tone of instruction being offered. Other alternatives to "teachy" could include words like tutelary, instructional, or educative. Whatever term you use, just make sure to use it tactfully to avoid offending anyone.