Out of context that nickname doesn't seem that bad. In context, it's very embarrassing.
Poor Howard! He gets some of the worst nicknames. He was an astronaut called Froot Loops! And, now he has to live with Clogzilla at least for a few weeks. Sheldon was right, that's not gonna pass.
That moment when Emily realized how she knew Howard was awkward. The experience at Emily's was probably one of the biggest humiliations of his life. Well, at least, the biggest that didn't involve his mother. I'm sure he has plenty of those. Emily will be a constant reminder of that night.
Despite that, I hope she sticks around. The Raj in this episode was much more self-assured and fun to see.