how do you deal with someone who deliberately tries to make you feel small?

You think I don't
know you sleep on the
other siiiiiiide
of the waaaall

CAUSE I'M COMIN THROUGH THE WALL
YEAH I'M COMIN THROUGH THE WALL
IN YOUR VERY OWN CAR
GONNA CRUSH YOUR GUTS
CAUSE I'M COMIN THROUGH THE WALL
YEAH I'M COMIN THROUGH THE WALL
WITH MY FIST IN THE AIR
GONNA HEAR YOU SCREEEEEEEAAAAAAM

etc.
it's a start

Seriously, is this someone who's worth the brain power to think about? If not, dismiss him/her to stew in his/her negative karma.

once you allow them to make the comments, ie, dont refute what they do, just like, ok whatever, no problem, it makes them rather pointless. ie, think to yourself "its important to this person to do this, why not let them". never show any annoyance, never refute them or defend yourself.
make it that they are the only one taking part in the exercise, that they are the only one putting in any effort

BUT! if you care about this person in any shape or form you have a tougher job. i mean, you want to make them irrelevant reall,y but if you want them to stay relevanet because you care about them, thats a harder path

next time though...grrrr

What you do, is cut them out of your life. Just ignore them. They are lint. Get yerself a fabulous new boyfriend/girlfriend/friend/S.O. and when the annoying person finally cottons on that you don't care about them, they will come running after you. And it will be too late. Hah!

Of course, the grown up thing would be to put to good use the assertiveness training my work sent me on a couple of years ago but screaming CUNTFACED WANKER down the phone is much more fun.

...they'll take...a metre.

One: the physical - basically use your body to intimidate and threaten, or give yourself an advantage in a confrontation. I'm not talking about smashing them to the floor with a cudgel but you can antagonise someone by closing the physical proximity between you. Either total eye-contact or total non-eye contact and slow measured breathing can also unnerve. When you blink, do it with purpose. Stay as still as possible and any movement should be deliberate and measured. Don’t fidgit or shift about. Slowly clench your fist perhaps or flex an ankle if you are seated, basically what your are communicating is that you are in control of your feelings at this time but also you are not someone to be fucked with, as there is a fire inside that you are comfortable about unleashing. Keep your mouth shut and clench your jaw so that your antagonist can see the muscles in your neck tense. Don’t be afraid or timid, sit or stand upright and don’t fold your arms or legs, a defensive posture, you want to try and use your body to suggest the possibility of physical retribution if they go too far. If they lay a finger on you tell them firmly and quietly to take their hands off you, and if they start waving their arms around, swearing or getting really animated ask them politely to please calm down. If all else fails, and if you can get away with it, a show of force might keep an opponent at bay, and certainly give them cause to think more carefully in future – the headbut being the most devastating psychological blow you can strike. Or there’s always the cudgel…

Two: Mental of course. Firstly say as little as possible – let fucko fill the gaps and silences with whatever shit they are spewing, if you are lucky and they are not too bright, as most people who go out of there way to make people feel small are, then they will shoot their own foot off without you having to say too much at all. If they do happen to start talking nonsense, ask them calmly to explain their last sentence. Getting them to repeat any more outrageous statements they make is another method of underming the validity of what they are saying. A smile in such circumstances is a useful weapon too, as it pisses people off if they are trying to be righteous, and once you start pissing them off, you can prize the initiative from them or at least take some satisfaction from the exchange. When you do speak, stick to the subject and do not go on a tangent or get distracted. Don’t ‘err’ or uhm’ and use your words sparingly. Don’t give anything unnecessary away with long excuses but don’t be unhelpful. Address any issue they bring up directly and succinctly and stay mildly pleasant throughout the exchange. They will try and interrupt you in which case state firmly that you wish to finish your sentence and keep your voice low and steady; this will put your antagonist off balance because if they are loosing it, they will become more acutely aware of this, and they will also have to make an effort to hear precisely what you are saying. Don’t be cocky or arrogant but be sure of your position. If they wander off subject, point this out and explain calmly with raised eyebrows that in this instance, you don’t think what they have just said is particularly relevant. This is sure to enrage but if you are occupying a sure position, it’s a fair gambit to employ.

If someone is trying to take you apart in front of others, if you remain calm, stand tall, and speak clearly, it is likely that they will be the one to look like a dick, not you. If its something going down at work, you can ask to have a witness present as you uncomfortable with some of the things being said, which immediately will give your antagonist cause for thought.

In the case of a more, shall we say, informal, disagreement, a good insult or a threat is always a classic. Tell your antagonist quietly that you’d like to continue this fascinating debate but unfortunately, the stench of their bad-breath is leaving you in need of fresh air, or that if they don’t shut their stinking maw of mouth, you might have to take a spanner to their teeth. Attacking personal deficiencies and exploiting insecurities is ruthless but effective. A bald man is going to be very touchy about their lack of hair for example. You can be subtle about such things, and just drop words pertaining to their lack rather than pointing it out directly. Stare at their gleaming dome or bushy eyebrows or sweating palms. If it’s a major insecurity, they’ll instinctively pick up on it and start to feel uncomfortable. If there are other people around, they are likely to realise what is going on and laughter is a valuable ally. Get the crowd on your side a keep them there with a calm, agile wit.