This is how I would rate all that everyone has been mentioning, and my rationale: worst offense to least
intoxication of any form (drugs legal and not, etoh)--no matter how good you are and used to the effects, you ARE NOT. period. studies have been done of reaction times. you endanger yourself and others. irresponsible beyond belief.
HIV, Hep C---ONLY a problem if you get blood on someone. and if you do, you owe them a warning. otherwise not a factor. irresponsible only if you indisciminately bleed on others and don't warn them.
Tobacco smoke/perfume--these can trigger asthma attacks in some people...wash off the odor before you walk on the mat.
Other communicable diseases (cold, flu, etc)--stay off the mat, you'll make others sick---a lot more likely than spreading HIV, just not as deadly, but still not nice.
Long nails (toe or otherwise)---obvious reasons, along with jewelry.
Questionable hygiene--odors can distract others, outright dirt is almost as risky if not more as the known cold... here I'd also put the women who wear makeup that rubs off on my gi...
It is sad that people doing Aikido care so little for other in the dojo that they would put their own selfish pleasure or desires over the health and safety of others.