I pulled out this used book I bought called "Mexican Slang: A Guide" by Linton H. Robinson, and this is what it says:
1. "No seas gacho" is "Don't be a drag" or "Come off it." (p. 19)
2. One frequently hears "No seas sangrón," or "No seas pesado" for "Don't be a pain in the ass." (p. 20)
Well, if you're in Mexico and some parts of the Chicano Southwest, these expressions might work for you.