Originally Posted by wphamilton

Lightweight == low body mass.
teetotaler == someone who abstains, will be more affected by small quantities.

No opprobrium, just the facts. I don't think either of these could be construed as something wrong with someone.

There are also, more rarely, other physiological conditions but I didn't mention them. One beer is not going to be an impairment for most people. It's a tempest in a teapot.