Once flew with a crew out of the east coast of Oz who definitely wouldn't have gone out the o/w of a 737. Lucky for them I guess they never seemed to get rostered on it...!
The 2 times I was rostered with this person I was literally sitting with one butt cheek off the double jumpseat since they took up 3/4 of it! Reason for ground duties if you ask me.
Havig said that, if the original question is, "am i too big to be a flight attendant", I have flown with girls about a AU size 16 who could fit in it no problem. Over that you might start to have issues. It does depend on aircraft type though, generally the smaller the aircraft the smaller the crew need to be!