Humour, especially about religion, politics etc can be quite funny, but can also be perceived as a "Vindictive Barb".
The problem with knowing when to draw the line is that there may be 2 lines. The speaker may have a line that he/she won't cross and the listener may have a line that he/she won't find humourous. All is well providing the lines are at the same level. Sometimes they're not and somebody's feeling will get hurt. Usually the hurt will fade away and be forgotten unless the barbs are repetitive.Then it can get ugly.
I love to laugh at and tell Irish jokes, but only with my irish friends, we all understand each other and the intent is known.
I can laugh at non Irish people telling Irish jokes as well but can get sullen if that line is crossed. it's very high by the way, so I don't often take offense.
I did get upset one night with one particular guy who has the mistaken idea that he is funny, He would love to be funny but he is not, anyway one night in a small folk club he introduced me by saying " this next act comes from Belfast, where they use rubber bullets, but next year they are going to use real ones". He was not the only one who laughed, there was quite a few hearty guffaws throughout the audience. I quietly explained to them what a rubbber bullet looked like, and to emphasise the type of damage that they can do I also told them a true story about a good friend of mine who had recently been hit in the head with one and died, and another family friend had been hit with one and lost both her eyes, then I calmly picked up my banjo and went home. believe me the laughter stopped, so there is a definite threshold than should not be crossed. If you are unsure of how far you can go then don't go , There are lots of topics that can be humourous without touching on politics, religion, colour, height, weight or nationality. When I came to Canada my workmates were in stitches about a pair of Canadian comics who had a weekly TV show, I watched the show every week looking for the humour and never once heard anything funny (to me), by the same token I loaned a canadian friend a record of an Irish comedian who I thought was hilarious, but he did not see anything funny either, so I suppose some humour s local and not transportable., while other humour is universal.
Intent is tangible, saying I didn't really mean that after the fact is sometimes hard to swallow, especially when it's the 3rd or 4th time you have had to say it to the same person(s). I relate Humour ito potatoes, some like them boiled, some like them french fried, others like them baked or roasted, but nobody likes them overdone. ?.
But it is impotnt to be able to laugh at ourselves. Just keep it within bounds.

slan agus oiche maith anois.