According to Rener Gracie, here are the four "undesirable" training partners:
1. Smasher (the guy who uses 110% strength at all times)
2. Stencher (the guy / gal who stinks)
3. Sensei (the guy who is always teaching instead of just training)
4. Sniper (the guy who only rolls with girls)
By the way - I agree with each of these.