It's a different thing when it's not your kid, but IMHO with your own
child, you figure out very quickly what makes your toddler tick.
Isolation drives my two-year-old crazy -- I don't even have to do a time
out or remove her from the room, just pick her up and move her to the
other side of the room, and she bursts into tears. Some kids hate it
when you leave the room. Or when you physically restrain the offensive
foot/hand/etc.

IMHO the single most important thing about discipline is consistency.
In a way, it doesn't even matter what limits and rules you decide to set
for your household, as long as you enforce them swiftly and *every
single time*. Your friend's 2.5-year-old has already learned that his
parents don't enforce limits, so he's not going to listen to them. It
should only take a few times of testing where your boundaries are before
he'll start treating you differently, I bet.

Toddler discipline seems so foreign when you've only got a tiny baby,
but in reality, you will instinctively know when that line between wants
and needs starts to be crossed (sometime after about 12-15 months), and
it becomes easy to start saying no, setting limits, ignoring tantrums,
etc.

With someone else's toddler, I would (and have, dealing with kids who
hit or push at the playground) lift his chin up so he's looking into my
eyes, say *very* sternly, "NO KICKING," and immediately turn and walk
away. Hopefully in your situation, the firmness of your voice and
obvious disapproval will mortify the parents into jumping in. If it's
just you dealing with the situation, you can move on to a non-time-out
option if he does it again (like wrapping your arms around him and
holding him in your lap for 30 seconds -- picking him up and hauling him
off to another, more boring room -- taking away his shoes and walking
out of the room -- I'm guessing, without knowing anything about the
situation, that it's an attention thing, so removing him/you might be
more effective than giving him negative attention). The faster (and
more calmly) you react when he defies, the quicker it's going to sink in
to him that you won't stand for it, and his behavior should stop (with
you, at least).

There are a bunch of great books out there that can validate your own
parenting instincts about discipline, or give you some new approaches if
you need some ideas other than spanking to pull out of your tool box.
"The Secret of Parenting" by Anthony Wolf is a great one to start with.

Mary S.