Tell em all to STFU, Op. Personally, whenever I see someone sit with either max BI or that 100bb amount, I peg him as an online player, or at least a competent player, until I see otherwise.
I generally like to buyin about 70-75bb (140-150). This gives me plenty room to play some hands and take a beat or two before I reach in my pocket to top off. I figure I'll likely pick up a pot or two and and be at that magical 100bb soon enough, but 30% of it will be someone else's mone
Once you get below 40bb, you're generally too short to play effectively and should top off (or consider getting up).
Another thing I do is buy my whole stop/loss for the sesh before sitting*. Then, when I sit I can eyeball stacks and will likely put out an average stack so as not to attract undue attention.
* A bit of a derail, but this has other advantages:
- If I want to toss on another 20 or 30, it's no big deal
- I worry about looking like a fish by re-buying
- If I stack off, I can re-load right away
- No more chips = time to go. No temptations to say "aww, to hell with it" and pull out another hundo (or, horror of horrors, hit the ATM
- Easier to know my profit/loss for the night. If I buy 250-300 up front and cash out 450, I know right away I had an alright night.