A man buying his partner clothing such as underwear is acceptable.
A colleague at work buying you underwear is not! There are some items of clothing that are always fine - for instance, buying someone a scarf is always acceptable! Baby clothes make great presents as long as you get the right size, but it's always nice to offer the receipt in case they are the wrong size.
Baby clothes are usually bought by height and weight which is done into average age sizes.
This works for most babies unless they're very tall! For adults buying a sweater is a lovely thoughtful gift.
Bear in mind the person's taste though and don't go mad with crazy designs buying them something they won't wear.
Imagine someone before you buy them a gift - what jumpers have you seen them in? Have they ever expressed an interest in owning a particular type of jumper, or one made with a type of material? Buying underwear is something usually saved for those you have intimate relationships with.
Knowing the right size is easy - look at existing underwear you know fits them well and make a note of it.
If you can't find a size label then you'll have to ask or stick to an item of clothing that has more general sizes such as small, medium or large.
Socks and pants are a traditional gift for close family relatives - usually it's the mother who buys them for the whole family.
Dad getting socks again is a family joke in some homes but continues year after year.
Some female relatives may be happy for you to buy them general underwear such as tights, but many may not.
If in doubt don't buy underwear as a present! It's quite a personal thing that some people just don't like discussing or even thinking that other people know what they're wearing under their clothes.
There are some shops such as Marks and Spencer who have very good returns policy which means if you buy an item of clothing from them as a gift it can be returned easily.
This makes them a safe bet on the high street and online for buying presents from.
In summary acceptable gifts for everyone are socks, scarves and jumpers.
Stay away from lingerie and underwear as gifts when you're doing your Christmas shopping! If you're buying for your other half then buying underwear is perfectly acceptable and encouraged!